ENGINEERING 
LIBRARY 


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APPLIED 
AERONAUTICS 

—  THE  AIRPLANE  — 


i. 


PUBLISHED  BY 

AIRPLANE  ENGINEERING  DEPARTMENT 

McCOOK  FIELD,  DAYTON,  OHIO 

U.  S,  A, 


.iiijii|i»iii  1 1    mil    jiiji     I  I.  imi.»    I.. 


-j^!iB|!|l!'?^!.J-' 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 

GIFT  OF 

BALDWIN  M.WOODS 


i 


APPLIED  AERONAUTICS 

—  THE  AIRPLANE  — 


APPLIED 
AERONAUTICS 

—  THE  AIRPLANE  — 


First  Edition 
1918 


Published  by 

Airplane  Engineering  Department 

McCook  Field,   Dayton,  Ohio 

U.  S.  A. 


ll.n^in>  ermg 
Cv  libraiy 


PREFACE 

TODAY  the  subject  of  aeronautics  appeals  to  nearly  everyone,  due 
largely  to  the  wonderful  progress  which  has  been  made  in  the  de- 
velopment and  utility  of  the  airplane  since  the  beginning  of  the  war. 

Although  the  airplane  is  among  the  most  important  features  of 
modern  warfare,  yet  there  are  comparatively  few  comprehensive  texts 
which  the  beginner  in  aviation  can  readily  understand.  In  many  cases 
the  student  aviator  and  the  aero  mechanic  have  had  but  a  limited  tech- 
nical training  nor  have  many  of  them  been  specially  trained  in  nuithe- 
matics,  particularly  in  the  higher  branches.  Therefore,  many  of  the 
present-day  text-books  on  aeronautics,  which  the  aeronautical  engineer 
would  consider  quite  elementary,  are  very  difficult  for  the  beginner. 

Realizing  the  difficulty  under  which  the  beginner  labors,  the  Airplane 
Engineering  Department  felt  that  an  elementary  course  in  applied  aero- 
nautics and  practical  aviation  was  needed,  and  has  brought  forth  this 
volume  with  the  hope  of  filling  this  need,  primarily  for  the  instruction 
of  the  men  at  McCook  Field.  This  book,  however,  is  not  intended  as  a 
text  on  the  design  of  airplanes,  but  was  written  solely  with  the  thought 
of  imparting  a  clear  idea  of  the  principles  of  flight,  together  with  such 
other  practical  information  as  can  be  applied  readily  by  the  man  in  the 
shop  or  in  the  air. 

The  text  is  base<l  primarily  upon  lectures  given  at  the  U.  S.  Army 
School  of  Military  Aeronautics,  Ohio  State  University.  The  Technical 
Publications  Department  at  McCook  Field,  however,  has  rearranged,  re- 
classified and  rewritten  a  great  deal  of  the  text  matter  contained  in  these 
lectures  in  order  to  make  the  book  as  clear  and  instructive  as  possible. 
Some  of  the  lectures  as  given  by  the  instructors  have  been  split  up  into 
several  chapters,  and,  where  it  was  felt  that  certain  parts  of  these  lec- 
tures could  be  enlarged  upon,  the  Technical  Publications  Depai'tment 
has  taken  the  liberty  of  making  such  changes  as  were  thought  advisable. 
A  number  of  illustrations  and  diagrams  have  been  added  to  those  used 
by  the  instructors. 

The  Airplane  Engineering  Department  therefore  gratefully  acknowl- 
edges its  obligations  to  Mr.  H.  C.  Lord  for  various  sections  in  the  first 
chapter  on  the  theory  of  flight,  and  jointly  to  ^fr.  Lord  and  IMr.  O.  T. 
Stankard  for  a  large  part  of  the  chapters  on  instruments.    It  also  wishes 


527090 


Preface 

to  express  its  thanks  to  Mr.  ^\.  A.  Kiiiiilit  for  the  information  furnished 
by  him  on  riggino-  and  alignment  of  ])lanes.  These  men  are  instructors 
in  the  U.  S.  Army  School  of  Military  Aeronautics,  Ohio  State  University. 

It  is  hoped  that  this  book  will  assist  the  student  aviator  and  the  aero 
mechanic  in  getting  one  step  nearer  their  goals  as  efficient  and  experi- 
enced units  in  the  U.  S.  Air  Service,  and  if  it  accomplishes  this  result  the 
Airplane  Engineering  Depai-tment  will  feel  amply  repaid  for  its  efforts 
in  bringing  it  forth. 

Dayton,  Ohio,  IT.  S.  A.,  July  1,  1918. 


CONTENTS 

PU(JC 
Chapter  1 

Theory  of  FVujht 11 

Investigating  wind  action — Constant  values — Studying  action  of 
wind — Streamline  shapes — Head  resistance — Lift,  drift  and  angle 
of  attack — Suction  on  top  of  plane — Center  of  pressure — Cambered 
planes  —  Horizontal  flight  —  Engine  power  —  Power  to  climb  — 
Stability. 

Chapter  2 
Types  of  Machines       -------         37 

General  divisions — Dirigibles  and  balloons — Heavier-than-air  craft 
— Training  machines,  primary  and  secondary — Pursuit  planes — 
Reconnoissance  machines — Bombing  and  raiding  machines,  day 
and  night. 

Chapter  3 
Hhippiufi,  ruJodding  (uid  AssciiihJi)ifi  -  -  -         41 

Shipping  instructions  —  Marking  boxes  —  Methods  of  shipping  — 
Railroad  cars  used — Unloading — Method  of  loading  on  truck  — 
Tools  required — Unloading  from  truck — Unloading  uncrated  ma- 
chines— Opening  boxes — Assembling — Fuselage  and  landing  gear 
— Center  panel  and  wings. 

Chapter  4 
Rif/giug  --------  44 

Fuselage — Construction  —  Longerons — Struts — Fuselage  covering 
— Monocoque — Landing  gear — Struts — Bridge — Axle  box  or  saddle 
— Axle  and  casing — Wheels — Tail  skid — Shock  absorber — Wing 
skids — Pontoons  on  sea  planes— Flying-boat  hull — Wing  construc- 
tion —  Front  and  rear  spars  —  Ribs  —  Cap  strip  —  Nose  strip — 
Stringers  —  Sidewalk  —  Struts  —  Wire  bracing — Wing  covering — 
Dope — Inspection  windows — Stay  Avires  and  terminal  splices — 
Aircraft  wire — Strand — Aircraft  cord  or  cable — Terminals  and 
splices — Soldering — Turnbuckles — Locking  devices. 

Chapter  5 

Alignment  --------  58 

Fuselage  alignment — Horizontal  and  vertical  stabilizers — Landing 
gear  or  under-carriage — Center  wing  section — Wings — Lateral  di- 
hedral angle — Table  for  lateral  dihedral— Stagger  —  Overhang  — 
Rigger's  angle  of  incidence — Wash-out  and  wash-in — Overall  meas- 
urements— Aileron  controls — Elevator  controls — Rudder  controls 
— Notes  on  aligning  board. 


Contents 

Page 

Chapter  6 

(.'are  and  Inspection  -  -      .     -  -  -  -  70 

Cleanliness — Control  cables  and  wires — Locking  devices — Struts 
and  sockets — Special  inspection — Lubrication — Adjustment — Vet- 
ting or  sighting  by  eye — Mishandling  on  the  ground — Airplane 
shed  or  hangar — Estimating  time — Weekly  inspection  card  form. 

Chapter  7 

Minor  Repairs  -...---  76 

Patching  holes  in  wings — Doping  patches — Terminal  loops  in 
solid  wire — Terminal  splices  in  strand  or  cable — Soldering  and 
related  processes  —  Soft  soldering  —  Hard  soldering  —  Brazing- — 
Sweating  —  General  procedure  in  soldering  —  Fluxes  —  Melting 
points  of  solders. 

Chapter  8 

Instruments       ........  SO 

Compass — Magnetic  error — Variation  —  Deviation  • —  Correction — 
Napier  diagram  —  Heeling  errors  —  Magnetic  clouds  —  Aneroid 
barometer — Errors — Uses  —  Altimeter — Errors — Banking  meter — 
Air  speed  indicator — Incidence  indicator  —  Sperry  clinometer  — 
Automatic  drift  set — Bourdon  gauge — Radiator  thermometer. 

Properties  of  Varioii.^  Woods  .  .  .  .  103 

Chapter  9 

Nomenclature  for  Aeronautics  .  .  .  .  104 

Based  on  official  nomenclature  recommended  by  the  National  Ad- 
visory Committee  for  Aeronautics  and  definitions  used  and 
standardized  by  the  U.  S.  Army  School  of  Military  Aeronautics  at 
Ohio  State  University. 


APPLIED  AERONAUTICS 

—  THE  AIRPLANE  — 
Chapter  1 

THEORY  OF  FLIGHT 

Investigating  wind  action — Constant  values — Studying  action  of  wind — Streamline 
sliapes — Head  resistance — Lift,  drift  and  angle  of  attack — Suction  on  top  of  plane 
— Center  of  pressure — Cambered  planes — Horizontal  flight — Engine  power — Power 
to  climb — Stability. 

IN  THIS  age  of  mechanical  flight  everyone  is  interested  in  airplanes. 
But  very  few  people,  however,  clearly  grasp  the  underlying  principles. 
The  theory  involved,  nevertheless,  may  be  demonstrated  by  simple  exi)eri- 
ments,  so  that  the  reader  with  only  an  elementary  knowledge  of  mathe- 
matics and  mechanics  can  understand. 

The  simplest  principle  of  airplane  flight  may  be  demonstrated  by 
plunging  the  hand  in  water  and  trying  to  move  it  horizontally,  after 
first  slightly  inclining  the  palm  so  as  to  meet,  or  attack,  the  fluid  at  a 
small  angle.  It  will  be  noticed  at  once  that  although  the  hand  renmins 
very  nearly  horizontal,  and  though  it  is  moved  horizontally,  the  water 
exerts  upon  it  a  certain  amount  of  pressure  directed  nearly  vertically 
upwards  and  tending  to  lift  the  hand.  This  is  a  fair  analogy  to  the  prin- 
ciple underlying  the  flight  of  an  airplane.  The  wings  of  the  plane  are 
set  at  a  small  angle,  and  the  plane  is  pushed  or  pulled  through  the  air 
by  the  propeller,  which  receives  its  power  from  the  engine.  Tlie  action 
of  the  air  on  the  wings,  inclined  at  an  angle,  tends  to  lift  the  plane  just 
as  the  action  of  the  water  on  the  hand,  inclined  at  a  small  angle,  has  a 
tendency  to  raise  the  hand  out  of  the  water. 

Investigating  Wind  Action 

A  rough  form  of  apparatus  for  studying  laws  of  wind  resistance  is 
shown  in  Fig.  1.  The  arm  E  hinged  at  C  carries  a  rectangular  plaiu^  B. 
The  adjustable  weight  D,  supported  by  the  arm  F,  is  used  to  balance 
the  pressure  of  the  wind  from  the  blower  A.  The  pressure  exerted  on  the 
plane  B  can  then  be  measured  by  moving  the  weight  D  along  the  arm  V 
until  B  floats  with  the  wind. 

Professor  Langley,  in  another  experiment,  proved  that  we  can  inves- 
tigate the  action  of  the  wind  upon  various  forms  of  surfaces  as  well  by 
directing  a  current  of  air  of  known  velocity  against  the  surface  held  in 
position,  and  weighing  the  reactions,  as  we  can  by  forcing  the  plane  itself 


12 


APPLIED   AERONAUTICS 


throTigli  still  air.  The  special  apparatus  used  was  mounted  on  the  end  of 
a  revolvinii  arm  driven  by  a  steam  engine  as  is  shown  in  Fi.c  2.  The 
chronograph,  a  recording  instrument,  was  used  to  measure  the  velocity' 
or  number  of  revolutions  of  the  table  in  a  given  time. 

By  such  a  method  as  that  shown  in  Fig.  1,  and  that  of  Professor 
Langley,  it  is  easy  to  see  that  the  laws  of  pressure  and  velocity  can  be 
determined  readily.  Methods  such  as  these  have  been -used  in  determin- 
ing that  the  rvind  resistance  varies  as  the  square  of  the  velocity. 

In  other  words,  if  the  velocity  is  doubled  it  follows  that  the  resist- 
ance is  increased  four  times,  or  if  velocity  is  five  times  as  great,  the  wind 
resistance  is  twenty-five  times  as  large. 

Constant  Values 

It  would  therefore  seem  to  need  no  experimentation  to  prove  that  if 
we  increase  the  surface  B  (Fig.  1)  we  would  increase  the  pressure  in 
direct  proportion  to  the  increase  in  surface  area.  Now  if  we  were  to 
increase  both  the  velocity  and  the  area  of  surface,  we  would  increase  the 
pressure  proportionally  to  the  product  of  the  square  of  the  velocity  and 
the  area  of  the  surface.  Thus  if  we  were  to  raise  the  velocity  of  the  air 
three  times,  the  resistance  would  be  increased  nine  times,  and  if  we 
then  doubled  the  surface  we  would  double  the  resistance,  which  has 
alreadv  been  increased  nine  times,  making  a  total  increase  of  eighteen- 
fold. 


Fig.  1 — Elementary  apparatus  for  studying  huts  of  wind  resistance 


THEORY    OF    FLIGHT 


13 


3/c/e  £'/e\/'af''/b/7  of  ^/7/r//h^  >^r/?7 


Fig.  2 — Prof.  Langlei/'.'^  ajtimratus  for  inrcs!ti(i<itniii  irintl  action  on 
various  forms  of  surfaces 


14  APPLIED  AERONAUTICS 

There  is  still  another  factor  to  take  into  consideration  in  calculating 
wind  pressures,  and  that  is  the  shape  of  the  surface.  To  take  that  into 
account  we  must  use  what  is  called  a  constant,  the  value  of  which  is 
determined  by  experiments  for  each  particular  shape  of  surface. 

The  following  explanation  will  enable  one  to  see  very  clearly  the 
meaning  of  the  term  constant  and  how  its  value  is  determined.  First  let 
us  explain  the  term  formula  which  is  merely  a  sentence  tersely  ex- 
pressed. To  attempt  to  make  a  study  of  flight  without  formulae  would 
make  it  necessary  to  express  relations  between  quantities  in  long  para- 
graphs of  words  that  could  more  readily  be  stated  in  simple  equations. 
Thus  if  it  were  desired  to  state  the  rule  that  the  quantity  A  multiplied 
by  twice  the  quantity  B  is  equal  to  C,  the  formula  representing  this 

would  be : 

A  X  2B  =  C 

Each  letter  or  symbol  in  a  formula  represents  some  factor  that  is  sub- 
stituted when  its  value  is  known.  If  A  ==  16,  and  B  =  4,  then  C  =  128, 
since  the  rule  interpreted  reads :  16  X  8  =  128. 

Derived  and  empirical  equations. — The  term  equation  simply  means 
that  the  quantities  on  one  side  of  the  equal  sign  are  equivalent  or  equal 
to  the  quantities  on  the  other  side.  Equations  are  of  two  kinds,  derived 
and  empirical.  A  derived  equation  is  susceptible  to  proof,  by  use  of 
mathematical  processes ,  An  empirical  equation  is  neither  derived  nor 
proven.  It  is  merely  a  statement  of  the  results  of  experiment  regardless 
of  mathematical  proof. 

In  many  branches  of  engineering,  empirical  formulie  are  constantly 
used,  and  in  aviation  the  lack  of  a  satisfactory  basic  theory  of  air  flow 
makes  empirical  formulae  based  on  experiment  most  necessary.  Empir- 
ical formuhe  are  really  experimental  averages. 

The  term  constant  can  now  be  fully  explained  and  it  will  be  seen 
how  beautifully  it  works  out  in  a  formula.     It  is  often  found  necessary, 


PROJECTED 


Fig.  3 — IUustratin(j  ntcanhig  of  term  "projected  area"'' 

especially  in  an  experimental  field,  to  introduce  numerical  constants  to 
balance  the  two  sides  of  an  equation.  For  example,  the  pressure  on  a 
surface,  as  we  have  already  learned,  is  equal  to  a  constant  times  the  pro- 
jected area  of  the  surface  (see  Fig.  3)  times  velocity  squared,  or  express- 
ing the  same  quantities  in  a  formula, 

p  =  KSV= 

where  P  =  Pressure  S  =  Projected  surface  area 

K  =  Constant  Y'  =  Velocity  squared 


THEORY    OF   FLIGHT 


15 


The  exact  value  of  the  constant  K  for  any  surface  is  determined 
experinientally  by  wind  tunnel  tests.  So  valuable  have  wind  tunnels 
proven  for  such  determinations  that  several  of  the  larj-e  airplane  build- 
ers now  have  installed  them  in  their  plants. 

In  solving-  a  i)roblem  it  mi^ht  be  known  that  the  pressure  P  varies 
as  the  area  of  the  surface  and  the  velocity  scjuared,  but  we  could  not 
express  this  relation  in  an  equation  capable  of  solution  until  a  numerical 
value  for  K  is  determined  for  the  particular  shape  subjected  to  the  wind 
pressure,  such  as  the  shape  illustrated  in  Fig-.  3.  Each  different  shai)e 
of  surface  requires  a  different  value  for  K,  which  can  be  determined 
experimentally. 


From  Loening's  Military  Aeroplanes 

Fifj.  4 — HliowiiKj  forms  of  eddies  set  up  bij  various  shaped  surfaces  in 

air  currents 


The  majority  of  formula"  for  air  pressures  involve  constants,  and 
the  great  advance  in  desig-ning  during  the  past  two  years  may  be  traced 
directly  to  the  determinations  by  the  aerodynamic  laboratories,  of  bet- 
ter values  of  these  constants,  for  use  in  empirical  formulje.  So  when 
M,  Eiffel,  or  other  men  of  authority,  inform  us  that  the  constant  K  for 
a  flat  shape  is  .003,  we  accept  the  value  just  as  we  do  the  report  of  a 
chemist  who  tells  us  the  composition  of  an  alloy. 

Studying  Action  ot  Wind 

A  study  will  now  be  made  of  the  action  of  the  wind  ui)on  various 
surfaces.  Fig.  i  sho^vs  what  would  be  seen  if  the  air  were  filled  with 
smoke  or  other  particles  and  blown  from  the  blower  in  Fig.  1  past  the 
surface,  and  then  an  instantaneous  photograjjh  made.  You  will  note  how 
in  the  first  picture  the  air  is  piled  up  in  front  of  the  surface  and  how  it 
eddies  and  whirls  behind  it,  thus  showing  that  the  disturbance  extends 
far  beyond  the  actual  obstruction  itself.  Note  the  decrease  in  the  eddies 
in  the  cases  of  the  other  shapes  in  Fig.  4. 


16 


APPLIED   AERONAUTICS 


The  sphere  offers  less  obstruction  than  the  flat  plane,  and  the  two 
peculiar  shapes  at  the  bottom  offer  still  less.  Such  bodies  are  said  to  be 
streamline.  The  bii^-  end  is  the  advancing  end.  An  old  rule  for  the  de- 
sign of  a  whaling  ship  was  that  "it  should  have  the  head  of  a  cod  and  the 
tail  of  a  mackerel."  With  such  streamline  shapes,  K  is  much  smaller  in 
value  than  for  a  flat  square  plane. 

Parasite  Resistance 

A  picture  of  a  typical  airplane  is  shown  in  Fig.  (J.  Notice  that  all 
the  struts,  wires,  landing  wheels  and  the  fuselage  or  body  offer  resistance 
to  passage  through  the  air — a  resistance  which  must  be  overcome  by  the 
engine.  The  sum  total  of  the  separate  resistances  of  all  these  parts  is 
called  the  paraf^ite  resistance.  This  wastes  power  and  so  all  such  parts 
are  carefully  streamlined  wherever  possible. 


Fig.  5 — Ejcperiment  shoicinfj  lift  of  inclined  surface  in  air  current 

Xote  the  wings  or  aerofoils,  two  on  each  side,  one  above  and  one 

below,  and  at  the  rear  a  vertical  rudder  K  in  front  of  which  is  a  vertical 

fin  V,  and  the  horizontal  fin  H,  the  back  part  of  which  can  be  turned  up 

or  down  by  the  pilot.    The  effect  of  this  is  to  cause  the  macliine  to  point 

up  or  doAvn  and  thus  change  the  angle  at  which  the  relative  wind  strikes 

the  aerofoils.    This  change,  as  we  will  see,  has  much  to  do  with  the  flying 

of  the  machine. 

Lift,  Drift  and  Angle  of  Attack 

Thus  far  we  have  found  a  lot  of  things  about  an  airi)lane  which 
would  tend  to  prevent  its  flying.  XoSv  let  us  study  Fig.  5.  Here  Ave 
haA^e  a  plane  B  fastened  so  that  it  makes  a  small  angle  with  the  direction 
of  the  wind  from  the  blower  A.  The  arm  is  hinged  at  C,  and  balanced  by 
the  weight  D,  so  that  Avhen  the  movable  weight  W  is  pushed  back  to  C 
the  plane  B  will  be  slightly  too  heavy.     When  the  blower  A  is  started 


THEORY    OF   FLIGHT 


17 


N 


18 


APPLIED   AERONAUTICS 


the  plane  B  instantly  lifts  and  the  aniomit  oi"  this  lift  may  he  measured 
by  the  movable  weight  W.  If  Ave  replaced  this  model  by  one  exacth'  like 
it  except  that  the  plane  B  makes  a  much  smaller  angle  with  the  relative 
wind  we  would  find  that  the  movable  weight  W  would  have  to  be  much 
nearer  C  than  before.  This  simple  experiment  proves  the  existence  of  a 
force  which  tends  to  lift  the  plane  and  further  that  this  force  is  greater 
as  the  angle  is  increased.  This  angle  is  called  the  angle  of  uttack  that 
the  plane  B  makes  with  the  air  stream.  The  force  which  tends  to  raise 
the  plane  is  called  the  lift,  and  evidently  its  value  mUvSt  depend  upon  the 
profile  of  the  plane,  the  velocity  squared,  and  the  angle  of  attack. 

Besides  the  lift,  there  is  another  force  which  is  due  to  the  plane's 
velocity  through  the  air,  called  the  drift.  This  force  is  due  to  the  fact 
that  the  plane  itself  offers  resistance  to  forward  motion  through  the  air. 
In  Fig.  7.  A  represents  a  bubble  of  air,  BC  a  plane  moving  in  the  direc- 
tion of  the  arrows.  Xow  evidently  one  of  two  things  must  happen. 
Either  the  plane  must  force  the  bubble  of  air  down  or  the  bubble  of  air 
must  force  the  plane  up.  This  resistance  that  the  bubble  of  air  offers 
to  being  displaced,  as  we  have  seen,  depends  upon  the  square  of  the  veloc- 
ity with  which  it  is  forced  out  of  the  way.  The  total  resistance  offered 
by  the  bubble  to  the  movement  of  the  plane  may  be  represented  by  the 
force  P  acting  at  right  angles  to  the  surface  of  the  plane.  The  horizontal 
and  vertical  components  of  P  are  represented  by  D  and  L,  respectively. 


Fif/.  7  —  Illustrating  how 
lift  and  drift  result  from  the 
moving  of  an  inclined  surface 
in  direction  of  arrows 


If  we  were  to  let  the  air  force  on  the  surface  have  its  way,  it  would 
push  the  surface  upwards  in  the  direction  of  L  and  backwards  in  the 
direction  of  D  at  the  same  time. 

So  we  put  weight  on  the  surface,  enough  to  overcome  the  force  L, 
and  then  quite  logically  call  this  force  the  lift.  And  for  D,  we  push 
against  it,  with  the  thrust  from  a  propeller,  and  we  call  D  the  drift. 


THEORY    OF   FLIGHT 


19 


This  simple  exjdanalioii  enables  us  at  once  t(t  state  the  reason  wiiy 
flight  in  heavier-than-air  niaehines  is  possible.  By  pushing  the  inclined 
surface  into  the  air  with  a  horizcuital  force  D,  we  create  a  pressure  on 
the  surface  equal  to  P,  the  force  of  which  I)  is  the  horizontal  component. 
But  by  doing  so  we  have  also  created  the  other  component  L,  which  is  a 
lifting-  force,  capable  of  carrying  weights  into  the  air. 

Consideration  of  this  resolution  into  lift  and  drift  at  once  indicates 
that  the  characteristics  to  be  sought  for  in  a  surface  are  great  lift  with 
a  very  small  drift,  so  that  for  a  minimtim  expenditure  of  jiower  a  max- 
imum load  carrying  capacity  is  obtained. 

Apparatus  used  to  prove  existence  of  lift  and  drift. — An  apparatus 
used  to  demonstrate  the  existence  of  these  forces  is  shown  in  Fig.  8.  The 
inclined  plane  B  is  fastened  to  the  arm   S   hinged  to  the  carriage   C 


Fif/.  8 — Apparatus  provintj  c.fistence  of  hoth  lift  and  drift 

at  the  point  F.  The  carriage  rests  on  a  glass  plate  D  and  is  shielded 
from  the  wind  from  the  blower  H  by  the  screen  E.  It  is  found  that  when 
the  blower  is  started  the  plane  B  will  lift  and  the  carriage  C  moves 
slowly  backward  carrying  the  plane  with  it,  thus  jtroving  the  existence 
of  lift  and  drift.  The  screen  E  is  then  removed  and  it  is  found  that  the 
carriage  moves  away  very  rapidly  thus  showing  the  effect  of  the  added 
head  resistance  due  to  the  carriage  itself. 

Suction  on  Top  of  Plane 

The  flat  surface  is  seldom  used  for  the  aerofoils  of  an  airplane.  The 
f(»llowing  illustrations  and  explanation  will  help  to  show  the  reasons  for 
not  using  it. 

The  plane  P  (Fig.  9)  has  an  opening  at  O  connected  to  manometer 
^I.  while  on  the  under  side  is  a  similai-  o]iening  connected  to  the  man- 


20 


APPLIED   AERONAUTICS 


Fig.  9 — Dcrice  for  ntea.siiriiu/  coin ituratirc  air  pressures  on   upper  and 
lower  surfaees  of  an  inclined  plane 

ometer  N  tli rough  the  rubber  tube  T.  Wheu  the  blower  is  started  the  uiau- 
ometer  M  shows  suetiou  at  the  poiut  O  on  the  ui»i)er  side  of  the  i)lane  aud 
N  shows  pressure  on  the  under  side  of  tlie  phine.  In  other  words,  the 
plane  is  not  only  bh)wn  up,  but  it  is  sucked  up  as  well. 

This  is  very  effectively  illustrated  by  a  still  simpler  experiment. 
Fii>'.  10  sho^^•s;  the  plane  AB  of  heavy  cardboard  to  which  is  fastened  a 
light  strip  of  paper  at  the  ptunt  A  and  left  free  at  the  point  C.  When 
the  plane  is  placed  in  a  wind  blowing  in  the  direction  of  the  arrows  the 
paper  is  seen  to  be  drawn  up  to  the  position  AC  a>\ay  from  the  i)lane  AB. 


Fi(j.  10 — Hhon-i)i<j  suetion  on  top  of  ineJiiied  plane  irhe)i  e-rposed  to  n-ind 
current  in  direction  of  arrows 


THEORY    OF   FLIGHT 


21 


From  Loening's  Military  Aeroplanes 

Fifj.  11 — CoiHifdndiie  rt-sislaitcc  to  a<1ranccmcnt  of  a  fhit  ]tjnn<'  at 
carious  aufjles  of  attack 

Fig.  11  represents  smoke  pictures  of  a  flat  plane  in  fonr  different 
positions.  The  lower  right  hand  one  shows  the  plane  at  a  very  small 
angle  of  attack.  The  existence  of  tlie  vacnnni  at  the  npper  front  edge 
of  the  plane  is  very  evident. 

E.r  peri  incuts  at  Eiffel  Lahoratorji. — Fig.  12  sliows  the  result  of  accu- 
rate measurements  by  M.  Eiffel  of  the  suction  on  top  of  a  plane  and  the 


F^ressure  Curve  for 
Upper  \5i/rfc;cG 


/fe/af/ve  Mnd 


/^ressure  Curve  for 
L  o  wer  •3urface 


Fig.  12 — Prc.ssiti-e  diat/raiu  of  iip/K-r  and  loa'cr  .surfaces  of  iiicliunl  plane 


22 


APPLIED   AERONAUTICS 


Fifj.  13 — In  a  flat  plane,  center  of  pressure  C  moves  toward  the  Jeadinfj 
edge  A  as  the  angle  of  incidence  becomes  smaller 

pressure  underneath.  Furthermore.  Eiffel  has  shown  bv  recent  experi- 
ments that  when  the  angle  of  incidence  of  a  flat  plane  is  low,  the  value  of 
the  suction  on  the  upper  surface  is  considerably  more  than  that  of  tlie 
pressure  on  the  under  surface.  Thus  in  this  case  it  is  the  upper  side  of 
the  plane  which  contribiTtes  most  towards  the  creation  of  the  lift,  a 
function  increasing  as  the  angle  grows  smaller.  This  fact  shows  that  the 
profile  of  the  upper  surface  of  a  plane  has  as  much,  if  not  more,  impor- 
tance from  the  standpoint  of  the  value  of  lift  than  that  of  the  under 
surface. 

Center  of  Pressure 

In  Fig.  1,  it  is  evident  that  the  wind's  force  on  the  plane  B  could  be 
entirely  replaced  by  a  single  force  acting  at  the  center  of  the  plane.  The 
fact  that  this  point  would  be  the  center  of  the  plane  is  due  to  the  fact 
that  the  wind  strikes  the  ]»lane  aV)solnte]y  symmetrically.    On  an  inclined 


Fig.  14 — Location  of  center  of  pressure  on  flal  .surface  for  rarious  angles 

of  attacl: 


THEORY    OF   FLIGHT 


23 


plane,  however,  the  aetiou  of  the  wind  on  tlie  front  or  advancing-  edge  of 
the  plane  is  different  from  that  on  the  reai-  or  trailing  edge  of  the  plane, 
hence,  we  can  no  longer  say  that  the  center  of  pressnre  is  at  the  geomet- 
rical center  of  the  plane. 

The  resnlt  of  the  double  action  of  the  air-cui-rent  with  pressnre  below 
and  suction  above,  both  unecjually  distributed,  is  that  the  total  reaction 
on  the  plane  is  applied  at  a  point  C  (Fig.  13)  nearer  to  the  leading 
edge  A  than  to  the  trailing  edge  B.  This  point  C  is  called  the  center  of 
pressure  of  the  plane.  In  a  flat  plane,  C  moves  toward  the  forward  edge 
as  the  angle  of  incidence  becomes  smaller,  until  when  the  angle  is  zero 
it  reaches  the  point  A. 

Tlie  curve.  Fig.  14,  shows  the  position  of  the  center  of  pressnre  on  a 
flat  plane  for  different  angles  of  attack.  It  will  be  noticed  that  from 
15  deg.  to  0  deg.  the  center  of  pressure  moves  very  rapidly  towards  the 
front  of  the  plane  A.  Tlie  wind  is  supposed  to  be  blowing  from  the  right 
in  a  direction  perpendicular  to  AB.  Airplanes  almost  never  fly  with  an 
angle  of  attack  greater  than  15  deg.  This  change  in  position  of  the  center 
of  pressure  very  easily  can  lie  pro^•eu  hy  a  well-known  and  very  simjile 


^ 


c 


B 


C 

Fig.  15 — Center  of  pressure  locatet]  close  to  foncard  echje  of  canlhonnl 
strip  used  in  simple  experiment 


experiment.  If  we  take  a  strip  of  light  cardboard  about  8  in.  long  by  1^ 
in.  wide  we  know  that  the  center  of  gravity  will  pass  through  the  geo- 
metrical center.  Now  if  we  were  to  project  this  through  the  air  in  a  hor- 
izontal position  with  the  long  side  forward,  the  center  of  pressure  being 
at  the  front  end  and  acting  upwards,  while  the  weight  at  the  center  of 
gravity  acts  downwards,  a  couple  would  be  produced  causing  the  plane  to 
rotate  with  the  advancing  edge  going  up.  This  shows  that  the  center  of 
pressure  is  near  the  front  edge. 

We  cannot  change  the  center  of  pressnre  but  we  can  change  the  po- 
sition of  the  center  of  gravity  by  placing  a  small  lead  weight  on  the 
front  edge.  Then  if  the  corners  at  A  and  B,  Fig.  15,  are  turned  slightly 
upwards  while  the  whole  is  given  a  lateral  dihedral  angle  as  shown  in 
the  lower  iiart  of  Fig.  15.  the  plane  on  being  projected  in  the  air  is  seen 
to  glide  almost  perfectly.  A  little  practice  is  necessary  in  adjusting  the 
weight. 


24 


APPLIED   AERONAUTICS 


F'reS'Sore  Curve  for 
Upper  3urfacG 


D/ reef /on  of 


Re/afive  Wind 


pressure 


Anc^le  of  Incidence 

F'ressure  Curve  for 
Lower  Surface 


Fig.  1(3 — Pressure  diagraiii  for  upper  and  loirer  fares  of  curved  surface 
u-'ttJi  inclined  chord.     ('oiiip(rre  witJt  Fig.  12 


of 
6 en  ^er  of  f^ressurG 


D/recfon  of 
f^e/afve  W/nd 


Fig.  17 — Location  of  center  of  pressure  on  a  curved  surface  at  various 
angles  of  attack,      (.'oiujiare   irittt   Fig.   11 


THEORY    OF   FLIGHT 


^:5 


Figs.  1(5  and  17  show  pressures  and  the  path  of  the  center  of  pressure 
for  a  curved  surface.  It  will  be  noted  first  how  greatly  the  suction  effect 
on  the  tojj  of  the  plane  has  been  increased,  and  that  from  zero  to  15  deg. 
(see  Fig.  17)  the  center  of  pressure  moves  in  exactly  the  reverse  direction 
from  the  way  it  does  in  a  flat  plane.  This  latter  effect  has  a  very  im- 
portant bearing  when  we  come  to  stability. 

Cambered  Planes 

Fig.  18  is  a  rough  sketch  of  what  one  might  call  a  typical  wing  sec- 
tion. Note  the  <lifference  in  ])rofile  between  the  top  and  bottom  surfaces. 
The  chord  may  be  defined  as  the  straight  line  which  is  tangent  to  the 
under  surface  of  the  aerofoil  section,  front  and  rear,  and  the  miglc  of 
attdcl-  as  the  angle  between  the  relative  wind  and  the  chord  of  the  aero- 
foil. We  may  write  the  following  simple  expression  for  the  lift  and 
the  drift : 

The  Lift  (L)   =  K^y^ 
The  Drift   (D)   =  L/r. 


l/f/ 


Dnff   /       Tro///n^ ^doe- 


'/eofAffoc/i 


Fig.  IS — Sl'ctch  of  a  typical  wing  section   icith  avronuutical  terms 

indicated 


The  coefficient  kj^  depends  upon  the  shape  of  the  aerofoil  and  the  angle  of 
attack  and  must  be  determined  experimentally.  The  quantity  r,  also 
determined  experimentally,  is  called  the  lift-drift  ratio  and  measures 
the  efficiency  of  the  aerofoil. 

Fig.  19,  gives  two  curves  for  an  aerofoil  of  the  section  shown.  The 
first  curve  gives  the  values  of  the  quantity  kL  for  different  angles  of  at- 
tack, while  the  second  cur^  e  gives  the  values  of  the  lift-drift  ratio. 

For  example,  suppose  that  an  airplane  with  aerofoils  of  the  ty])e 
shown,  lifting  surface  60  s<|.  ft.,  is  flying  at  an  angle  of  attack  of  11  deg.. 
and  with  a  velocity  of  70  m.p.h.     What  will  be  the  lift  and  the  drift? 

Fr(mi  the  chart.  Fig.  19,  we  find  that  for  this  type  of  plane  and 
angle  of  attack  kj^  =  0.0028  and  r  =:-  11,  hence, 

L  =  ki.SV-  =  0.002S  X  60  X    (70)=  =  823  lbs. 


D 


823 

=  75  lbs. 

11 


26 


APPLIED   AERONAUTICS 


CMARACrE/^/^5T/C  ^ECT/ON   OF 
A£ROrO/L 


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0°  r  a°  3°-^"  .5""  e^  7°a°  &"  /(r/r/2''/3r/^r/sve''/T/8''/9''2o'' 

A  NGLE  or  /rs/C/OBNCE  OF  W/As/G  CHORD 

Fig.  19 — Curves  slioir'nif/  values  of  Ul  and  Lift/Drift  ratio  for  a  fypieal 

icing  section 


THEORY    OF   FLIGHT  27 

Tf  now  wi'  cliaiiue  the  angle  of  attack  to  3i  dei''.,  keeping  the  surface 
and  vt'kK'ity  the  same,  we  find  from  the  chart  that  k^  =  0.0014  and 
r  =  13.5,  hence, 

L  =  kLSV=  =  0.0014  X  60  X    (70)=  =  412  lbs. 

L  412 

D  =  =  =  30  lbs. 

r  13.5 

Horizontal  Flight 

For  horizontal  flight  the  lift  produced  by  the  machine's  velocity 
must  at  all  times  exactly  equal  its  weight.  For  if  the  lift  were  less  than 
the  weight  of  the  plane  would  fall,  while  if  the  lift  were  greater  than 
the  weight  the  machine  would  begin  to  climb.  We  therefore  can  replace 
the  lift  by  the  weight  W.     Then  we  would  have  for  horizontal  flight : 

Weight   (W)  =  kLSV- 
and  the  drift   (D)   =  W/r. 

For  example,  a  given  airplane  weighs  I  with  load)  1800  lbs.  Its  aero- 
foils are  of  the  type  illustrated  and  the  lifting  surface  is  120  sq.  ft. 
What  will  be  its  velocity  for  horizontal  flight  at  an  angle  of  attack  of 
12deg.? 

From  the  chart,  Fig.  10,  we  find  that  for  this  type  of  plane  and  angle 
of  attack,  kL  =  0.0029,  whence, 

L  =  W  =  kLSV^  or  1800  =  0.0029  X  120  X  V- 

1800 

transposing,  V^  =-- =  5172 

.0029   X   120 

hence,  V  =  >/5172  =  72  m.p.h. 

If  now  we  reduce  the  angle  of  attack  to  5  deg.,  the  chart.  Fig.  19, 
shows  that  kL  becomes  0.00175,  whence, 

1800  =  0.00175  X  120  X  V= 

1800 

transposing,  V-  =  =  8572 

0.00175   X   120 


hence,  V  =  yy8572  or  92+   m.p.h. 

The  above  example  illustrates  this  important  priuci])le  that,  since 
a  machine  in  horizontal  flight,  except  for  a  slight  loss  due  to  consump- 
tion of  gasoline,  maintains  a  constant  weight  and  a  constant  surface  and 
since  k^  for  a  given  plane  de])ends  solely  upon  tlic  angle  of  attack,  the 
V'elocity  for  horizontal  flight  is  completely  determiued  Avheu  we  know 
the  angle  of  attack.  Xow  since  the  pilot  can  control  the  auglf  of  attack 
by  means  of  his  elevators  he  can  control  the  velocity  for  horiz(Uital  fliglit. 


28 


APPLIED   AERONAUTICS 


Fig.  20  shows  four  different  positions  of  the  plane  corresponding- 
to  four  different  angles  of  attack.  In  each  case  the  machine  is  flving 
horizontally,  though  at  first  sight  one  might  think  that  in  position  4  the 
machine  was  climbing. 


Fig.  20 


FOUR  POSITIONS  FOR  FLIGHT 

(1)  Minimum  angle. — This  is  the  smallest  angle  at  which  horizontal  flight  can  be 
maintained  for  a  given  power,  area  of  surface,  and  total  weight.  The  minimum  angle 
gives  the  maximum  horizontal  flight  velocity  at  low  altitude.  Note  that  the  propeller 
axis  is  inclined  slightly  downwards  when  flying  at  this  angle. 

(2)  Optimum  atngle. — This  is  the  angle  at  which  the  lift-drift  ratio  is  highest.  In 
modern  airplanes  the  propeller  axis  is  generally  horizontal  at  the  optimum  angle,  as 
shown  at  (2)  in  the  above  figure.  Note  that  in  the  position  shown  the  velocity  of  the 
airplane  will  be  less  than  when  flying  at  the  minimum  angle.  The  effective  area  of 
wings  and  angle  of  incidence  for  the  optimum  angle  are  such  as  to  secure  a  slight  climb- 
ing tendency  at  low  altitude 

(3)  Best  climbing  angle. — This  angle  is  a  compromise  between  the  optimum  and 
maximum  angles.  Modern  airplanes  are  designed  with  a  compromise  between  climb 
and  horizontal  velocity.  At  this  angle  the  difference  between  the  power  developed  and 
the  power  required  is  a  maximum,  hence  the  best  climb  is  obtained  at  this  angle. 
See  Fig.  22. 

(4)  Maximum  angle. — This  is  the  greatest  angle  at  which  horizontal  flight  can  be 
maintained  for  a  given  power,  area  of  surface  and  total  weight.  If  the  angle  is  in- 
creased over  this  maximum,  the  lift  diminishes  and  the  machine  falls. 


It  would  seem  at  first  that  we  have  entirely  neglected  the  engine, 
especially  as  there  is  a  general  impression  that  the  yelocity  of  a  machine 
depends  upon  the  power  of  the  engine,  while  as  a  matter  of  fact  the  form 
of  wing  sections  together  with  the  plane's  dimensions  are  equally,  If  not 
more,  important.     In  tlie  preceding  discussion  we  have  simply  assumed 


THEORY  OF  FLIGHT 


29 


that  tlie  eii.uiiic  liad  tlic  necessary  powci-  t(»  iiiaiiitaiii  the  ]»hiiie  at  sucli  a 
vehx-ity  as  was  (h'teniiined  l)y  that  aiiule  of  attack  at  wiiicli  the  i»ih>t 
drives  the  maeliiue. 

Engine  Power 

The  power  of  any  enjiiue  is  measured  by  the  velocity  at  which  it  can 
move  a  body  against  a  ^ven  resistance,  and  its  nnit.  the  horsepower,  may 
be  define<l  as  the  power  re(|nired  to  lift  one  pound  ;j8,(MI()  ft.  in  one  min- 
ute or  375  miles  in  one  lionr,  or  the  powei-  i-ecpiired  to  lift  375  ponnds 
one  mile  in  one  lionr. 

We  must  therefore  multiply  the  total  resistam-e  offered  to  the  air- 
plane, which  consists  of  the  drift  plus  the  jtarasite  resistance  multiplied 
by  the  velocity  of  the  machine,  and  divide  the  result  by  375  to  get  the 
horsepower  required.     Or.  written  as  a  formula  : 


(Drift  +  Parasite  Resistance)    X  Velocity 


Horsepower. 


From  the  above  expression  for  horsepower,  it  will  l)e  noted  that  since 
the  drift  for  a  given  machine  depends  solely  upon  the  angle  of  attack, 
and  the  parasite  resistance  depends  upon  the  square  of  the  velocity,  which 


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FUl.  'll—Yulue  of  kj^  <ind  Lift  Drift  ratio  for  <i  f/ircn  iiidrhinc 


30 


APPLIED   AERONAUTICS 


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Fig.  22 — Shoiving  poioer  required  at  different  angles, 
also  power  delivered 

in  turn  depends  upon  the  angle  of  attack,  we  may  state  that  for  a  given 
machine  with  its  load,  the  horsepower  is  completel}^  determined  when  we 
know  the  angle  of  attack  at  which  the  machine  flies. 

Fig.  21  corresponds  for  the  entire  machine  to  Fig.  19  for  the  aerofoil 
itself  and  gives  the  value  of  k^  for  a  given  machine,  as  well  as  the  lift- 
drift  ratio. 

Fig.  22  gives  in  the  heavy  curve  the  power  required  to  drive  the 
machine  at  the  angles  of  attack  marked  on  the  curve,  which  correspond 
to  the  speed  in  miles  per  hour  given  at  the  bottom.  The  other  set  of 
curves,  four  of  them  dashed  and  one  a  light  line,  give  the  power  delivered 
to  the  machine  by  the  engine  through  the  propeller.  The  latter  would 
be  straight  horizontal  lines  were  it  not  for  the  fact  that  the  efficiency 
of  the  propeller  varies  Avith  the  velocity  of  the  airplane.  The  ordinates 
as  shown  on  the  left  side  of  the  diagrajn  correspond  to  horsepower. 

Let  us  consider  the  case  where  the  engine  is  making  1200  r.p.m.  It 
will  be  seen  that  if  the  pilot  changes  his  elevators  so  as  to  fly  with  an 
angle  of  attack  of  a  little  less  than  1  deg.,  or  of  a  velocity  of  about  82.5 
m.p.h.,  he  will  be  using  every  particle  of  power  that  his  engine  can  de- 


THEORY    OF   FLIGHT 


31 


liver  at  that  speed.  Any  slight  decrease  in  the  angle  of  attack  will  ( jiiisc 
him  to  go  down  probably  in  a  nose  dive.  As  he  increases  the  angle  of 
attack  we  come  to  a  point  where  the  distance  between  the  two  curves, 
power  delivered  and  power  required,  is  the  gi'eatest.     Here  we  will  have 


(2*120"^    21'"       SZ'T^     23"^      24f"    25"^     26^     27"^     26^     29'"     30"^ 
F\(j.  I'o — ^<Jioiciiig  rapid  cliaiif/cs  in  ici)id  vclocit//  i)i  sitort  sixiccs  of  time 

the  greatest  excess  of  po\\er  over  that  used  for  horizont^il  flight,  all  of 
which  can  be  nseil  in  climbing.  Hence  that  ]H)int  will  be  the  position 
for  maximum  rate  of  climb.  It  is  indicated  by  the  vertical  dash  line 
marked  maximum  climb  at  an  anjile  of  attack  of  a  little  less  than  6  deg. 


12 


APPLIED   AERONAUTICS 


or  a  velocity  of  a  little  over  55  m.p.li.  Increasing  his  angle  of  attack 
still  further,  or  at  about  8  (leg.,  which  is  the  lowest  point  on  the  curve, 
where  the  horsepower  required  for  horizontal  flight  is  only  30,  we  get 
a  point  of  most  economical  flight.  Tlien.  as  we  decrease  the  angle  of 
attack,  the  power  required  rises  rapidly  until  at  40  m.p.h.  the  two  curves 
cross  again  and  any  increase  in  the  angle  of  attack  would  cause  the  ma- 
chine to  stall  in  the  sense  of  going  down,  which  might  take  the  form  of 
either  a  nose  dive  or  tail  slip.    It  is  well  to  compare  this  with  Fig.  20. 


F'kj.  24 — Calculation  of  power  required  to  rVunb 


It  is  also  interesting  to  compare  this  with  Fig.  23,  taken  from 
Langley's  The  Stored  Euergi/  of  the  Wind,  and  which  illustrates  the 
rapid  changes  in  the  velocity  of  the  wind  occurring  in  short  intervals  of 
time.  The  vertical  lines  represent  spaces  of  one  minute  and  the  horizon- 
tal lines  wind  speeds  differing  by  4  m.p.h.  It  will  be  noticed  that  between 
32  and  24  min.  the  wind  fell  from  about  37  m.p.h.  to  12  m.i).h.  and  rose 
again  to  38  m.p.h.  On  account  of  the  momentum  of  the  airplane  it  would 
be  practically  impossible  for  its  actual  velocity  to  change  with  anything 
like  that  rapidity,  and  as  the  lift  depends  upon  the  square  of  the  velocity 
it  is  evident  that  the  pilot  would  experience  a  series  of  ''bumps"  when 
the  velocity  increased,  and  momentary  drops  when  the  velocity  decreased. 
The  feeling  has  been  likened  to  a  motor  boat  driving  rapidly  through  a 
choppy  sea. 

Power  to  Climb 

Suppose  the  center  of  gravity  of  a  machine  be  moving  in  the  direc- 
tion AB,  Fig.  24,  with  a  velocity  of  V  miles  per  hour.  The  horsepower 
will  then  be  the  sum  of  two  components,  viz.,  that  necessary  to  overcome 
the  wind  resistance,  as  already  given  for  horizontal  flight  and  that  neces- 
sary to  lift  the  machine  through  the  distance  CB  in  the  time  required  for 
the  machine  to  travel  fiom  A  to  B.  Now  if  AB  be  taken  to  represent  the 
distance  the  machine  travels  in  an  liour,  BC  would  then  represent  the 
velocity  of  climb.  The  power  consumed  in  climbing  is  equal  to  the 
product  of  the  weight  of  the  machine  in  pounds  by  the  velocity  of  climb 
in  miles  per  hour  divided  by  375.  Let  us  call  AB/BC  the  climbing  ratio 
R  which  gives  us  BC  =  AB/  K  =  V/R.  We  will  have  then  the  i>ower 
expended  in  the  climb  alone  equal  to  WV/R,  and  the  total  horsepower 
becomes : 


THEORY    OF   FLIGHT 


33 


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Fifi.  25 — SJi(nr'uif/  Jioir  drift,  ixtraxiic  resistance  and  </Jidiii(/  motion 
depend  npon  amjle  of  attack 

(drift  +  parasite  resistance )V  WV 

Horsepower  = + 


375  R 


The  case  of  special  interest  is  where  the  horsepower  becomes  zero. 
This  is  the  condition  when  the  engine  is  shnt  off  on  a  glide. 
When, 

(drift  +  parasite  resistance )V  WV 

h   =  0,     this  reduces  to 

375  375  R 


W 


R  =  — 


(drift  +  parasite  resistance) 

It  should  be  noted  that  the  value  of  R  is  negative,  due  to  the  fact 
that  the  machine  is  gliding  toward  the  earth.  Now  since  both  drift  and 
parasite  resistance  depend  upon  the  angle  of  attack,  the  gliding  velocity 
and  slope  depend  upon  the  angle  of  attack,  and  are  under  the  control 
of  the  ]>il(>t.    This  is  illustrated  in  Fig.  25. 

Stability 

One  of  the  most  important  considerations  in  an  airplane  is  stabiliiv. 
which  is  generally  considered  under  three  headings,  viz..  longitudinal, 
lateral  and  directional. 


34 


APPLIED   AERONAUTICS 


Para//e/  to  Chore/ 
'of  Lokver  H^/r?^ 


1 


/Jspecf  /^ah'o  =3-  =3 
/J spec/-  /Pa//o  ='-§=j-^ 

ASPECT  PATJO 


-3fag(jer 
STAGGER  onc/DECALAGE 


GAP 


LA  TERAL  D/HEDRA  L  anc/  SPAN 


^  r-A/ig/i?  o/'/nc/c/ence 


D/hec/ro/ 


LONG/TUD/NAL  D/HEDPAL 

Fif/.  2(J — niiistnit'tiH/  iiictiiiiii;/  of  .some  (icntiKniticul  fcfmH 


THEORY    OF   FLIGHT 


35 


\  CenferofFre^^ure 


Center  cfn-e^ure 


Ceo^rof/^re^3e/rc 


Cenferof 


FUj.  -7 — llic  center  of  pressure  of  u  flat  phiiie  mores  forintnl  as   the 
angle  of  incidence  is  decreased 


Center  of Pre^ssure 


Center  of/^re&surc 


Center 
of  Pre-ssure 


Fi(j.  28 — T'/ze  center  of  pressure  of  a  ciirred  surface  mores  foru-ard  uitJi 
decreasiuf/  (uu/Jes  of  iucidence  up  to  aJtout  12  deg.  Below  this  <iii(/Je  it 
reverses  uud  uiores  toward  the  center  Uf/ain 


Ano/e  of  Incidence  6  Deoree^       '•'^z:Ay/eof/nc/dencG  2  Decrees 
Main  Surface 


D/recfion  of  Mof/on  -^ 

Angle  of  /ncfder>ce  reduced 
/Deqree    to  /  Dearee    — 


f5tabiliz/ng 
Surface 


"D/recf/on  of 
Mot/on 


~Anole  of  Incidence  reduced 
/De^ee   to  ^  Degrees 


"^D/recfion  ofMof/on 

Fi<j.  21) — Jllusfratiuf/  hou'  the  rear  surface  Jias  its  auiiJe  of  incidence 
reduced  in  f/reater  proportion  than  does  the  front  surface  ndien  the  com- 
hi  nation  is  tipped  dou-uirard 


36 


APPLIED   AERONAUTICS 


Loii(/itii(Jin<iJ  siaJ/ilitji. — Tliis  stability  is  needed  to  keep  the  airplane 
from  pitching  nose  downward  or  tipping  backward,  nose  up  and  tail 
(h)wn,  whenever  a  gust  or  eddy  is  encountered. 

Flat  surfaces  are  longitudinally  stable  because,  as  shown  in  Fig.  14, 
the  center  of  pressure  moves  toward  the  leading  edge  as  the  angle  of 
incidence  is  decreased.  Fig.  27  sIionms  four  positions  of  a  flat  surface 
moving  from  right  to  left.  Gloving  horizontally  as  in  posithm  A  the  cen- 
ter of  pressure  is  at  the  leading  edge,  and  when  in  the  vertical  position  I) 
the  center  of  pressure  coincides  with  the  transverse  center  line  of  the 
surface.  However,  suppose  the  surface  to  be  moving  as  at  C  and  a  sudden 
gust  of  wind  tips  it  into  position  B  with  a  lesser  angle  of  incidence.  Then 
the  center  of  pressure  moves  forward,  introducing  a  greater  moment  and 
tending  to  force  the  plane  back  into  its  original  position  (\  On  the 
other  hand,  if  the  surface  assumes  too  great  an  angle,  the  center  of  pres- 
sure moves  back  and  tlie  rear  is  forced  up,  causing  the  surface  again  to 


NORMAL    POS/T/ON 

A  equa/s  8 


T/PPED  POS/T/ON 

A  qrea/er  /h^r?  3 


F'kj.  30 


resume  its  original  position  C.  Thus,  if  it  were  not  for  the  fact  that  the 
flat  surface  has  a  very  poor  ratio  of  lift  to  drift,  it  could  be  used  in  air- 
planes to  advantage,  due  to  this  inherent  longitudinal  stability. 

Next  consider  Fig.  28,  giving  three  positions  of  a  cambered  surface, 
which  has  a  much  greater  lifting  etticienc^-  than  a  flat  surface.  It  is  also 
supposed  to  be  moving  from  right  to  left.  In  position  C  the  center  of 
pressure  coincides  with  the  transverse  center  line.  Supposing  this  sur- 
face to  be  moving  in  attitude  V>  with  the  center  of  pressure  at  approx- 
imately the  position  indicated.  If  it  is  suddenly  tipped  into  jtositiou  A, 
it  will  be  seen  that  the  front  part  has  a  negative  angle  of  incidence, 
which  results  in  a  do\\nward  i)ressure  on  this  portion.  The  center  of 
pressure  of  the  surface  being  the  resultant  of  all  forces  acting,  it  is  obvi- 
ously affected  l)y  this  action  at  the  front,  and  moves  backwards.  If 
the  surface  is  tipped  still  further,  the  backward  nunemeut  of  the  center 
of  pressure  is  increased  and  therefore  there  is  still  less  tendency  to  push 
the  front  up,  Avhen  such  a  tendency  would  l»e  utost  desirable.  On  the 
other  hand  if  the  auule  of  iuci<leu<'e  becomes  suddeulv  ureater  than  the 


THEORY  OF  FLIGHT 


Z7 


iioniml  position  li,  the  pressure  on  the  front  ed-c  decreases  and  the  re- 
sultant center  of  j)ressure  moves  forwai'd,  thus  tendinj>  to  push  the  front 
up  and  .i;ive  the  surface  a  still  <>reater  an^le  of  incidence. 

Therefore,  it  is  necessary  to  have  some  way  of  compensating;  foi-  this 
instability  of  cambered  surfaces,  and  this  is  done  by  the  use  of 'an  auxil- 
iary stabilizing;  surface  somt^  distance  back  from  the  main  surface  and 
set  at  a  lesser  anj>le  of  incidence  than  the  main  surface.  Such  a  stabilizer 
is  a  necessary  feature  of  all  modern  airplanes.  Fi"-.  29  shows  two  such 
surfaces  in  tandem,  thus  formiui-  an  elementary  aiiplane.  (\>nsider  the 
airplane  to  be  traveling;  horizontally  with  the  an^le  of  incidence  of  the 


■T^erf/cc?/  Ax/s 


W/hc/ 


Verf/ca/  /y'n 


Fifj.  30A — Diafjnnii  to  show  action  of  fcrticd]  fin  in  preserrinr/ 

directional  stafiilitij 

main  surfaces  (>  deo-.  and  the  lear  one-third  of  this,  or  2  de.u.  Xow  sup- 
posing a  sudden  gust  pitches  the  plane  into  some  such  position  as  shown 
in  the  lower  part  of  the  diagra.m.  The  angle  of  incidence  of  both  surfaces 
is  now  reduced  say  1  deg.,  the  main  surface  being  at  a  5  deg.  angle 
and  the  rear  surface  at  1  deg.  In  other  words,  the  main  surface  has  lost 
only  about  IT  percent  of  its  angle  of  incidence,  whereas  the  stabilizer 
has  lost  50  percent,  ronsecjuently  the  stabilizer  has  lost  more  of  its  lift 
than  the  main  surface,  and  it  therefore  must  fall  relative  to  the  position 
of  the  main  surface,  bringing  the  combination  back  into  normal  position 
again.  On  the  other  hand,  if  the  front  of  the  ])lane  is  suddenly  forced  up, 
the  stabilizing  surface  receives  a  relatively  greater  increase  in  angle  of 


38  APPLIED  AERONAUTICS 

iucidence  than  the  main  surface,  lienee  relatively  greater  increase  in  lift, 
causing-  the  hack,  end  of  the  plane  to  be  brought  up  until  the  combination 
again  is  normal. 

Lateral  stahUity. — This  stability  is  necessary  to  prevent  the  machine 
from  rolling  about  its  horizontal  axis.  It  is  difficult  to  secure,  but  is 
often  promoted  by  having  a  slight  lateral  dihedral  angle  between  the 
upper  wing  surfaces,  as  shown  in  Fig.  30.  Should  the  airplane  suddenly 
be  tipped  to  one  side,  in  the  position  shown  to  the  right  of  the  diagram, 
the  planes  on  the  dov.n  side  become  more  nearly  horizontal,  whereas, 
those  on  the  other  side  assume  an  angle  still  greater  than  they  had  when 
flying  normally.  Thus,  the  effective  projected  lifting  surface  on  the 
side  A  is  increased  and  that  on  side  B  is  decreased,  briugiug  the  i)lane 
back  to  its  normal  lateral  position.  Other  features  are  introduced  to  aid 
lateral  stfll)ility,  such  as  "wash  in"  on  the  left  side  to  give  this  side 
slightly  more  lifting  ability  to  compensate  for  the  torque  of  the  propeller. 

Directional  stahUltji. — Sucli  stal)ility  aids  in  keeping  the  plane  on 
its  course.  In  order  to  prevent  ya^^■ing  with  every  gust  of  wind,  the 
vertical  tail  fins  present  on  nearly  all  modern  ])lanes  are  used.  Kefer- 
ring  to  Fig.  30  A,  suppose  a  sudden  gust  of  wind  to  deflect  the  airplane 
from  its  normal  course  A  so  that  the  nose  points  off  the  course  to  the 
pilot's  left,  as  indicated  by  the  dotted  lines  in  position  B.  This  swings 
the  tail  around  to  the  right  so  that  the  right  side  of  the  vertical  fin  pre- 
sents a  flat  surface  to  the  wind  pressure  resulting  from  the  tendency  of 
the  machine  still  to  move  forward  in  the  direction  A,  due  to  its  inertia, 
even  though  it  is  temporarily  pointing  in  direction  B.  A  moment  with 
arm  r  is  thus  set  up,  which  tends  to  swing  the  plane  back  on  its  vertical 
axis  until  the  fin  is  again  parallel  to  the  direction  of  the  relative  wind. 
The  action  is  similar  to  that  of  a  wind  vane,  the  vertical  fin  of  which 
always  keei>s  it  pointing  in  the  direction  of  the  wind. 


Chapter  2 

TYPES  OF  MACHINES 

General  divisions — Dirigibles  and  balloons — Heavier-than-air  craft — Training  machines, 
primary  and  secondary — Pursuit  planes — Reconnoissance  machines — Bombing  and 
raiding  machines,  day  and  night. 

ALL  aircraft  arc  divided  into  two  iicneral  classes:  heavier  tlian  air 
and  lighter  than  air.  In  tlie  li.uliter-than-air  class  (  which  <-onsists 
of  aircraft  snpported  in  the  air  Ity  the  Itno.vancy  of  a  ii'as,  li.uhter  than 
the  ail-  it  displaces,  contained  in  a  jias  l)aii  <»f  some  convenient  fornii.  a 
further  snh-divisiou  may  he  made  into  diriiiihles,  or  craft  e(|uipped 
with  a  power  plant,  propeller  and  vertical  and  horizontal  rn<lders.  so 
that  they  can  he  operated  and  steered  at  the  will  of  the  pilot,  and  hal- 
loons,  or  craft  not  fitted  with  any  means  of  propulsion  or  steei-in<>-, 
and  which  therefore  drift  with  the  wind  unless  held  captive  hy  means  of 
a  cahle  anchorinii'  them  firmly  to  a  point  on  the  liround. 

Diriiiihles  are  further  divided  into  three  types,  the  rijiid,  the  semi- 
rigid and  the  non-riiiid,  all  three  of  which  are  being-  used  to  a  consider- 
al)Ie  extent  in  the  present  war.  The  Z(^])i>elin.  which  has  ])roven  such  a 
costly  failure  for  Germany,  is  the  outstanding  example  of  the  rigid  con- 
struction. The  Blimp  as  used  so  successfully  by  the  British  in  coast- 
guard observation  and  anti-submai-ine  work,  and  as  being  made  in  this 
country,  is  a  good  example  of  the  non-rigid  type.  There  are  several  ex- 
anijiles  of  the  semi-rigid  construction,  such  as  the  German  Parseval  and 
others. 

In  the  balloon,  or  non-dirigible  class,  the  captive  observation  balloon 
and  particularly  the  kite  type  balloon  are  being  employed  to  a  consider- 
able extent,  even  though  they  may  fall  an  easy  prey  to  enemy  airi)lanes 
unless  strongly  protected,  ^^'ith  improved  methods  of  i)rotection,  by 
means  of  anti-aircraft  barrage,  the  employment  of  winches  which  rapidly 
pull  the  captive  balloon  to  cover,  and  a  thorough  protective  patrol  by 
scouting  airplanes,  the  balloon  as  a  means  of  reconnoissance  and  for  long 
distance  artillery  observation  has  come  into  increased  favor.  Important 
improvements  are  also  being  attempted  by  using  non-inflammable  gas 
in  the  balloon,  or  by  fitting  a  protective  housing  consisting  of  an  outer 
baa'  containinu'  an  inert  "as  such  as  nitronen. 


40  APPLIED  AERONAUTICS 

In  any  case  the  observer  in  a  captive  balloon  is  always  equipped 
with  a  parachute  ready  for  immediate  use  in  case  the  balloon  should  be 
destroyed  by  the  enemy  by  any  means  before  it  could  be  pulled  down. 

Aircraft  Heavier  Than  Air 

There  are  four  types  of  heavier-tlian-air  machines:  airplanes,  kites, 
helicopters  and  ornithopters.  Only  one  of  these,  the  airplane,  for  prac- 
tical reasons  is  worth  considering  at  this  time.  This  type,  bein<>-  of  gi'eat- 
est  importance  will  be  studied  botli  from  the  standpoint  of  its  uses  and 
its  constructional  features. 

Airplanes  for  military  use  are  divided  into  five  i>eueral  types:  train- 
ini>-,  pursuit,  combat,  reconnoissance  and  bond)ino  or  raiding-. 

Traiuuu)  machines  are  either  primary  or  secondary.  The  former  is 
used  in  elementary  training  and  is  generally  of  the  dual  control  type, 
so  as  to  allow  the  instructor  to  control  the  machine  until  the  pupil  be- 
comes accustomed  to  the  "feel"  of  it,  under  the  guidance  of  an  experi- 
enced pilot,  then  take  over  the  control  gradually,  and  to  allow  the  in- 
structor to  correct  mistakes  of  the  pupil  before  they  can  have  serious 
consequences.  Machines  called  "rollers"'  or  "penguins,"  having  curtailed 
wings  to  prevent  them  actually  rising  off  the  ground,  are  also  used  in 
primary  instruction.  Secondary  school  machines  are  generally  similar 
to  those  used  for  actual  fighting  work ;  this  being  particularly  true  of 
scout  or  pursuit  nmchines  for  "stunt''  flying.  Training  machines  should 
be  easily  handled,  should  possess  marked  inherent  stability  and  should 
have  a  fairl}^  slow  get-away  speed.  A  familiar  machine  used  in  this 
country  has  the  following  characteristics : 

Tractor  biplane 
Two  seater 

Horsepower — 80  to  120. 
Radius  of  flight— 200  mi. 
Rate  of  climb — 300  ft.  per  min. 
Minimum  flying  speed — 45  m.p.h. 
Maximum  speed — 75  m.p.h. 

In  France  and  England,  quite  a  number  of  Farman  and  B.  E. 
pusher  machines  are  used  for  training,  and  for  advanced  work  the  Nieu- 
port  Scout,  the  Bleriot  monoplane  and  similar  machines  are  used,  espe- 
cially in  French  schools. 

Pmsiiit  planes. — This  class  comprises  the  fastest  and  most  easily 
handled  machines  that  it  is  possible  to  produce.  Their  offense  depends 
on  speed  and  their  defense  on  ability  to  maneuver.  Due  to  the  great 
strains  imposed  in  "stunt"  flying,  the  monoplane  has  lost  favor  on  ac- 
count of  structural  weakness.  The  ^lorane  monoplane  which  is  still  in 
use  is,  however,  an  exception.  The  Nieuport  one-and-one-half  plane, — 
probably  the  most  successful  pursuit  machine — the  Spad,  the  English 
Bristol  and  the  Sopwith  scouts  are  all  popular  with  Allied  aviators.   The 


TYPES  OF  MACHINES  41 

prime  requisites  for  scouts  are  speed,  ability  to  climb  ami  power  to  ma- 
neuver. Scouts  may  be  either  sinjile  or  two-seaters.  They  always  carry 
one  <»un  either  fixed  and  firin*;  tlirouj^h  the  propeller  or  on  tlie  upper 
plane.  Other  gun  mountings  may  be  used,  however,  especially  when  an 
extra  passenger  is  carried.  The  princiijal  characteristics  of  scouting 
machines  are : 

Tractor  biplane 

Horsepower — above  150 

One  or  two-seater 

Kadius  of  fligiit— 300  mi. 

Kate  of  cliud> — over  800  ft.  per  min. 

Minimum  flying  speed — 50  m.p.h. 

Maximum  speed — 150  m.p.h. 

Ceiling— 20,000  ft. 

Combat  itKicliiiirs. — Airplanes  of  the  combat  type  are  used  exten- 
sively for  strictly  fighting  i)urposes,  and  are  essentially  the  same  as  the 
reconnaissance  type  machines  except  that  they  are  stripped  of  wireless 
equipment,  photographic  apparatus  and  other  accessories  not  essential 
for  fighting  purposes.  The  combat  machine  is  a  two-seater  and  carries 
four  guns,  two  in  the  observer's  cockpit,  and  movable  on  a  circular  track 
surrounding  the  cockpit,  and  the  other  two  fixetl  and  synchronizi^l  to 
fire  between  the  propeller  blades  and  operated  by  the  pilot.  These  ma- 
chines usually  have  a  ceiling  of  between  20,000  and  23,000  ft.  and  carry 
oxygen  tanks  for  the  passengers.  They  are  of  the  tractor  biplane  type, 
and  considering  their  weight  and  fighting  ability,  have  .remarkable 
maneuverability.     The  principal  features  of  combat  planes  are : 

Tractor  biplane 
Horsepower — 250  or  more 
Two  passengers 

IJadius  of  flight — 300  miles  or  more 
Kate  of  flying— 10,000  ft.  in  10  min. 
31inimum  speed — 50  m.p.h. 
^Maximum  speed — 150  m.p.h.  or  over 
Ceiling— 20,000  to  23,000  ft. 

The  recoil nois.w nee  machine. — This  type,  usually  carrying  an  ob- 
server, wireless,  photographic  apparatus  and  sometimes  a  number  of 
light  bondis  is  usually  armed  with  one  or  two  machine  guns.  The  pur- 
pose of  this  type  is  to  do  various  forms  of  scout  and  observation  work 
both  above  and  behind  the  lines,  and  also  contact  patrol  work.  These 
machines  fly  at  altitudes  of  from  2,000  to  0,000  feet  and  usually  rely 
on  the  pursuit  machines  for  ju'otection.  This  class  of  machines  is  one 
which  comprises  a  large  assortment  of  constructions.  They  are  gener- 
ally biplanes,  pusher  or  tractor,  and  quite  often  with  single,  double  or 
triple  motors.     The  armament  consists  generally  of  two  machine  guns. 


42  APPLIED  AERONAUTICS 

one  mounted  fixed  and  firing  ahead,  tlie  other   niovahh^  and  operated  by 
the  observer.     The  general  (jualities  of  these  phxues  are  as  f oUows : 

Biplanes — tractor,  pusher  or  combination 
Two  passenger  or  more 
Horsepower — 200  or  over 
IJadius  of  flight — 300  mi.  or  over 
Kate  of  clind) — 200  ft.  per  min.  or  over 
Mininmm  flying  s])eed — 50  m.i).li. 
^Maximum  speed — 110  m.p.li.  or  over 

BomhiiKi  or  r(ti<1iii(/. — These  machines  are  large,  slow,  weight-carry- 
ing planes.  In  order  to  get  the  latter  quality,  a  biplane,  triplane  or  even 
a  multiplane  construction  is  necessary  since  there  is  a  limit  to  the  span 
of  wings.  Parasite  resistance  is  high  and  horsepower  must  necessarily  be 
large.  This  form  of  machine  is  rather  new  and  has  been  developed  dur- 
ing the  i-ecent  war,  because  of  its  wonderful  possibilities,  and  it  is  only 
reasonable  to  suppose  that  very  nuirked  improvements  will  conu^  in  the 
future.  The  larger  Handley-Page  (British)  bombers,  and  tlie  Italian 
Caproni  triplanes  are  an  indicarion  of  what  developments  are  being  made 
in  raiding  machines.  If  the  Allies  are  successful  in  clearing  the  air  of 
German  j)lanes,  any  destruction  or  offensive  operations  must  be  accom- 
plished by  the  bomber.  The  extent  of  damage  which  might  be  inflicted 
in  this  way  is  limited  only  by  the  nuudter  of  machines  and  the  amount  of 
bombs  dropped.  These  planes  rely  on  the  accompanying  pursuit  planes 
for  protection.  Paiding  or  bombing  exj)editious  are  always  carried  out 
in  fornuition  and  the  number  taking  part  is  unlimited.  The  character- 
istics likewise  are  without  limit. 

The  principal  features  of  the  large  boud)ing  planes  are  as  follows: 

Biplane,  Triplane 

Horsepower — no  upper  limit.      (As  many  as  five 

engines  are  being  used. ) 
Xund)er  of  passengers — from  two  up 
Kange  of  action — over  300  mi. 
Weight  carried — above  1000  lbs. 
Bate  of  climl) — 250  ft.  per  min.  and  over 
^lininnnn  flying  speed — 45  m.p.h. 
Maximum  speed-— up  to  85  m.p.h. 
Ceiling— 10,000  ft. 

A  further  classification  of  day  and  night  bombers  is  made.  Night 
work  is  dependent  on  suitable  lighting  signaling  arrangements,  proper 
landing  signals  and  the  ability  to  reckon  position  in  the  dark.  The  Ger- 
mans have  given  considerable  attention  to  this  branch  and  it  is  also  bfeing 
practiced  by  the  Allies. 


Chapter  3 

SHIPPING,   UNLOADING  AND   ASSEMBLING 

Shipping  instructions — Marking  boxes — Methods  of  shipping^ — Railroad  cars  used — Un- 
loading— Method  of  loading  on  truck — Tools  required — Unloading  from  truck — 
Unloading  uncrated  machines — Opening  boxes — Assembling — Fuselage  and  landing 
gear — Center  panel   and   wings. 

^HJPPIXG  iii-sf ructions. — Boxes  in  \vlii<h  airplanes  or  parts  tliere<jf 
^    are  sliijjped  should  l)e  marked  with  the  followinji': 

Destination,  or  name  and  address  of  eonsiijnee  in  full. 

Sender's  name. 

Weiulit  of  l)ox  (<»TOSs,  net  and  tare). 

('nl>i('  contents  (or  lenj>th,  widtli  and  heiiiiht). 

Box  and  shipment  nnmlier. 

Hoistiiiii'  center. 

"This  side  np." 

}f('tliO(]s  of  sJtipiiiii!/  iiHtcliiiK's.  —  Machines  are  shipped  cither  hy 
loadinu  in  a  railroad  car  withont  cratini*,  or  by  crating  in  two  boxes. 
In  the  latter  case  the  win^s,  center  section  panel,  tail  snrfaces,  landinii 
geiu'  and  propeller  are  removed  from  the  fnselaije,  and  the  fnselai»e,  land- 
iiii»  j.iear,  propeller  and  radiator  are  packed  securely  in  the  fnselaiie  box. 
The  other  parts  are  packed  in  the  panel  box.  All  aerofoil  sections  are 
stood  on  their  enterin<»-  edi^es  and  secnrely  padded  to  protect  their  cover- 
ing's.   Stmts  are  stood  on  end. 

If  the  machine  is  not  to  be  crated  only  the  followiiiii  i)arts  are  re- 
moved— winii's,  center  section  panel,  tail  surfaces  and  jn'opcllcr.  The 
fnselai>e  is  loaded  into  the  railroad  car  and  allowed  to  rest  on  the  landiuj; 
ijear.  The  latter  should  be  blocked  np,  however,  to  take  the  l<»ad  off  the 
tires  of  the  iandinu  _i;var  wheels  and  off  the  shock  absorl)ers.  The  fiisel- 
aiie  iiinst  of  course  be  secnrely  fastened  in  the  car  to  ])revent  movement 
in  any  direction.  The  win«is  and  other  separate  ])arts  are  crated  aiiainsr 
the  sides  (►f  the  car.  The  win<is  are  secnre«l  with  their  entering;  wedues 
down  and  carefully  padded  to  prevent  damajie. 

Railroad  ears  asnl  for  tniiisporfatioii. — If  i)ossible  o]»en  end  or  aut(>- 
mobile  cars  are  used  for  transportation  of  airi»lanes.  Sometimes  with 
crated  machines  sondola   cars  are  used,  and   with   uncrated  machines. 


44  APPLIED  AERONAUTICS 

ordinary  box  ears  having  no  end  doors.  In  the  hitter  ease,  however,  it 
is  necessary  that  the  side  doors  of  the  railroad  car  be  as  wide  as  possible, 
to  allow  working  the  fuselage  in  and  out  without  damage. 

For  transporting  machines  (either  crated  or  uncrated)  from  the 
railroad,  a  flat  top  truck  is  used.  If  the  truck  is  short  it  will  be  necessary 
to  use  a  trailer  to  support  the  overhang  of  the  boxes. 

Unloading 

Metliod  of  Joadiny  on  truck. — Before  unloading  a  machine,  every- 
thing in  the  railroad  car  should  be  inspected  for  loss  or  damage.  If 
everything  is  O.  K.  proceed  with  the  unloading,  but  if  any  loss  or  damage 
is  discovered  report  fully  at  once  to  the  receiving  officer  and  await  his 
instructions  before  doing  anything  further. 

The  tools  required  for  removal  <»f  airplane  boxes  from  the  railroad 
car  are :  1  axe  or  hatchet,  2  crow  bars,  6  or  8  rollers  and  100  ft.  of  1  in. 
rope. 

The  cleats  holding  the  boxes  to  the  car  floor  are  first  removed  with 
the  axe  and  crow  bars,  and  the  panel  box  removed  from  the  car.  If  the 
fuselage  box  is  not  marked  to  show  which  is  the  front  end  it  should  be 
lifted  slightly,  if  possible,  first  at  one  end  and  then  at  the  other,  to  de- 
termine which  is  the  engine  end.  This  end,  being  the  heavier,  should 
come  out  first  if  possible. 

The  truck  is  backed  up  to  the  door  of  the  car,  rollers  are  placed 
under  the  fuselage  box  and  it  is  then  rolled  out  onto  the  truck.  The  rope 
is  now  used  to  fasten  the  box  to  the  truck.  After  this  is  done  the  truck 
is  moved  forward  slowly  and  the  box  is  thus  pulled  out  of  the  car.  If  a 
trailer  is  to  be  used  it  should  be  placed  under  the  box  before  the  latter 
is  taken  all  the  way  out  of  the  car. 

When  taking  the  fuselage  out  tail  end  first,  the  same  methods  are 
used,  except  that  the  light  end  is  blocked  up  ^^ilen  removed  from  the  car 
and  a  truck  is  put  under  the  heavy  end. 

When  moving  along  roads  care  should  be  taken  to  go  slowly  over 
rough  places,  tracks  and  bad  crossings.  It  is  also  a  good  policy  to  have 
a  man  on  each  side  of  the  box  to  watch  the  lashings  and  see  that  nothing 
comes  loose. 

Panel  Box 

The  wing  box  (or  panel  box)  is  removed  from  the  car  in  the  same 
manner  as  the  fuselage  box. 

Unloading  ho.res  from  triicl\ — For  this  work  2  planks  about  2  in.  x 
12  in.  X  12  ft.  long  should  be  used.  These  should  be  fastened  to  the  end 
of  the  truck  with  one  end  resting  on  the  ground,  so  that  they  will  act  as 
skids.  The  tail  end  of  the  fuselage  box  is  depressed  until  it  rests  on  the 
ground,  then  by  moving  the  truck  forward  carefully  the  box  will  slide 
down  the  planks  onto  the  ground. 

Unloadinf/  uncrated  machines. — In  this  case  all  of  the  smaller  parts 
should  be  removed  first.     Then  the  cleats  and  ropes  are  removed  which 


SHIPPING,  UNLOADING  AND  ASSEMBLING  45 

hold  the  inachiiie  in  the  oar.  Two  lon^  plauks  are  placed  from  the  door 
of  the  car  dowu  to  the  j^roimd  and  are  used  to  roll  the  machine  ont  of 
the  car. 

Open  ill  (J  })().i-es. — A  screw  driver  and  bit  brace  should  be  used  to  re- 
move the  screws  in  the  top,  sides  and  ends  of  the  box.  The  top  is  re- 
moved first,  then  one  side.  All  smaller  parts  of  the  machine  should  be 
taken  out,  after  which  the  remaining-  side  of  the  box  is  removed,  and 
lastly  the  ends. 

Asseiiihliitfj  a  machine. — The  landing  gear  should  be  put  on  first. 
To  do  this  the  fuselage  must  be  raised  by  one  of  two  methods.  The  first 
is  by  chain  falls  or  l)lock  and  tackle.  The  rope  sling  should  be  passed 
under  the  engine  sill  just  to  the  rear  of  the  nose  plate.  The  tail  of  the 
machine  is  allowed  to  rest  on  the  tail  skid  while  the  nose  is  raised.  The 
second  method  is  by  shims  and  blocking.  This  latter  method  is  the  most 
common  because  chain  falls  are  not  always  available.  Enough  blocks 
should  be  secured  to  raise  the  fuselage  high  enough  to  slip  the  landing 
gear  underneath.  The  tail  is  first  raised  l)y  2  men  and  blocks  are  i^laced 
under  Station  5  or  the  rear  wing  section  strut.  The  blocking  must  be 
directly  below  the  strut  and  must  have  padding  upon  it.  Then  the  tail 
is  depressed  and  another  block  is  put  under  the  forward  wing  strut.  This 
operation  is  then  repeated  until  the  fuselage  is  high  enough  for  the  land- 
ing gear  when  the  nmchiue  is  blocked  under  nose  and  tail  and  the  other 
l)locks  are  removed.  Three  or  four  men  are  all  that  should  l)e  required 
for  this  second  method. 

Assembling  Wings 

After  the  landing  geiir  is  assembled  the  center  section  panel  should 
be  attached  and  approximately  lined  up.  Then  the  wings  are  assembled. 
There  are  two  methods  for  doing  this;  one  is  to  put  on  the  top  i)lanes, 
place  supports  under  the  outer  edges,  then  put  in  struts  and  lower  planes 
and  connect  up  the  wires.  The  other  method  is  to  assemble  the  wings 
completely  while  on  the  ground.  Wings  are  stood  on  their  entering 
edge,  struts  are  put  in  and  wires  tightened  up  to  hold  the  wing  sections 
together.  Then  the  wings  are  attached  to  fuselage  by  turning  them  over 
and  attaching  the  top  wing  first,  then  the  lower  wing.  One  side  of  the 
machine  must  be  supported  until  the  opposite  set  of  wings  is  attache<l. 
After  wings  are  all  attached,  then  the  tail  surfaces  should  be  assembled 
to  the  body.  The  horizontal  stal»ilizer  should  go  on  first,  then  the  ver- 
tical fin.  rudder  and  elevators  in  the  order  named.  On  some  nuichines 
the  elevators  will  have  to  l)e  put  on  liefore  the  rudder.  After  everything 
is  assembled  the  machine  is  put  in  alignment. 


Chapter  4 

RIGGING 

Fuselage — Construction  —  Longerons — Struts — Fuselage  covering — Monocoque— Landing 
gear — Struts — Bridge — Axle  box  or  saddle — Axle  and  casing — Wheels — Tail  skid — 
Shock  absorber — Wing  skids — Pontoons  on  seaplanes — Flying  boat  hull — Wing 
construction — Front  and  rear  spars — Ribs — Cap  strip — Nose  strip — Stringers — 
Sidewalk  —  Struts — Wire  Bracing — Wing  covering — Dope — Inspection  windows  — 
Stay  wires  and  terminal  splices — Aircraft  wire — Strand — Aircraft  cord  or  cable — 
Terminals  and  splices — Soldering — Turnbuckles — Locking  devices. 

"O  IGGING  deals  with  the  erection,  alignment,  adjustment,  repair  and 
■■■^   care  of  airplanes. 

Airplanes  are  of  liiiht  skeleton  construction  with  parts  largely  held 
together  with  adjustable  tie  wires,  hence  they  easily  can  be  distorted  or 
their  adjustment  ruined  by  careless  or  improper  rigging.  The  eflficiency, 
controllaltility,  general  airwortliiness  and  safety  of  machine  and  pilot 
therefore  depend  very  largely  upon  the  skill  and  conscientiousness  of  the 
rigger. 

For  purposes  of  description  the  airplane  may  be  divided  roughly 
into  three  parts  ( exclusive  of  the  power  plant ) .  These  are  the  body  or 
fuselage,  the  wings  or  aerofoils  and  the  landing  gear. 

The  fuselage  is  the  main  structural  unit  of  the  airplane.  It  provides 
a  support  and  housing  for  the  power  plant,  contains  the  cockpit  for  the 
pilot,  and  the  instruments  and  control  mechanism.  The  rear  end  of  the 
fuselage  carries  the  rudder,  elevators,  stabilizing  fins  and  the  tail  skid. 
The  wings  or  aerofoils  are  attached  to  the  fuselage  through  suitable 
hinged  connections  or  brackets  and  the  fuselage  is  supported  by  the 
wings  when  the  machine  is  in  the  air.  Conversely  the  wings  are  sup- 
ported from  the  fuselage  when  the  airplane  is  on  the  ground,  as  in  that 
case  the  Mdiole  weight  of  the  machine  is  supported  by  the  landing  gear 
and  the  tail  skid,  liotli  of  which  are  attached  under  the  fuselage. 

The  body  or  fuselage  is  of  trussed  construction,  a  form  which  gives 
great  strength  and  rigidity  for  a  given  weight  of  material.  Parts  as- 
sembled together  in  the  form  of  a  truss  are  spoken  of  as  members.  Those 
which  take  a  thrust  only  are  called  compression  members,  while  those 
resisting  a  pull  are  known  as  tension  mend)ers. 

Other  members  may  be  either  tension  or  compression  members,  de- 
pending on  how  the  load  or  force  is  applied  to  them  at  any  given  time. 
There  are  also  members  subject  to  a  shearing  stress  and  others  to  cross- 
bending  or  compound  stresses. 


RIGGING  47 

The  fuselage  is  usually  coustnieted  with  four  main  louiiitudiiial 
iiieiiibers  inniiing  the  full  length.  These  are  called  longerons.  Thev  are 
,sei)arated  at  intervals  by  (•oiu})ression  niend)ers  termed  stmts.  The  whole 
structure  is  in  turn  tied  together  and  braced  by  means  of  diagonal  wires, 
fitted  with  turnbuckles  for  adjustment,  which  go  under  the  geiUMal  name 
of  wire  bracing  or-  stay  wires. 

Stay  wires  in  certain  parts  of  an  airplane  are  designated  as  flying, 
ground,  drift,  anti-drift,  etc.     These  will  be  considered  later. 

That  part  of  the  surface  of  the  fuselage  which  is  bounded  l)y  two 
struts  and  two  of  the  longerons  is  known  as  a  panel.  The  points  at  which 
the  struts  join  the  longerons  are  calh'd  ])anel  points  or  stations.  The 
cubical  space  enclosed  by  eight  struts  and  the  four  longerons  is  called  a 
bay.  Some  makers,  Curtiss  for  instance,  number  the  stations  in  the 
fuselage  from  front  to  rear  calling  the  extreme  front  station  No.  1.  Oth- 
ers, such  as  the  Standard,  nundier  these  stations  from  the  rear  toward 
the  front,  calling  the  tail  post  zero. 

The  longerons  are  made  of  well-seasoned,  straight-grained  ash.  They 
are  curved  inward  toward  the  front  end  and  usually  terminate  in  a 
stamped  steel  nose  plate.  This  is  true  particularly  of  airplanes  ecjuipped 
with  engines  of  the  revolving  cylinder  type.  The  nose  plate  is  stamped 
from  plate  steel  about  .10  in.  in  thickness.  This  plate  not  only  ties  the 
longerons  together  at  the  front  end  of  the  fuselage,  but  supports  one  end 
of  the  sills  on  which  the  engine  rests.  In  some  types  of  planes  it  also 
forms  a  bracket  for  sui)porting  the  radiator.  In  other  types  of  air])lanes 
the  longerons  may  terminate  at  the  front  end  of  the  fuselage  in  an  o])en 
frame  which  forms  the  supx^ort  for  the  radiator  and  also  supports  the 
front  ends  of  the  engine  bearers  or  sills.  The  two  upper  and  the  two 
lower  longerons  are  brought  together  in  pairs  one  al>ove  the  other  at 
the  rear  end  of  the  fuselage,  and  are  joined  to  the  tail  post  or  vertical 
hinge  post  on  which  the  rudder  is  mounted. 

Lightened  Construction 

In  order  to  lighten  the  construction  of  the  fuselage  as  much  as  pos- 
sible, the  rear  portions  of  the  longerons  are  often  cut  out  to  an  I  section 
and  spruce  is  often  substituted  for  ash  for  the  rear  half,  suitable  splices 
.strengthened  with  fish  plates  being  used  wherever  joints  are  nmde  in 
the  longerons.  It  is  possible  to  lighten  the  rear  portion  of  the  fuselage 
in  this  way  for  the  reason  that  this  part  of  the  body  does  not  support  as 
much  weight  or  undergo  as  severe  stresses  as  the  forward  portion. 

In  a  machine  of  neutral  tail  lift  (one  in  which  the  rear  horizontal 
stabilizers  are  set  at  such  an  angle  that  they  barely  sustain  the  weight 
of  the  rear  portion  of  the  machine  when  flying  horizontally  in  the  air  I 
the  stresses  in  the  longerons  are  exactly  the  opposite  when  the  machine 
is  in  the  air  to  those  obtaining  on  the  ground.  When  the  machine  is  at 
rest  on  the  ground  it  is  supported  near  the  front  and  i-ear  ends  of  the 
fuselage  by  the  landing  gear  and  the  tail  skid.  Tliis  metliod  of  su])port 
produces  tension  in  the  lower  longerons  and  compression  in  the  u])per. 


48  APPLIED   AERONAUTICS 

When  in  the  air  the  machine  is  supported  by  the  wings  which  are  attached 
to  the  fuselage  at  the  center  wing-  section.  The  system  of  supports,  trusses 
and  stay  wires  between  the  upper  and  lower  wings  transfers  most  of  the 
support  from  the  wings  to  the  center  panel  section  of  the  upper  wing.  This 
results  in  tension  in  the  upper  longerons  and  compression  in  the  lower. 
The  fuselage  struts  are  usually  made  of  spruce,  although  ash  is  some- 
times used.  The  struts  are  joine<l  to  the  longerons  by  means  of  metal 
clips.  The  construction  of  the  clips,  which  are  usually  bent  in  U  shape, 
is  such  that  each  forms  a  partial  socket  for  receiving  the  end  of  a  strut 
or  struts.  In  general,  struts  are  subjected  to  compression  only.  For  this 
reason  spruce  is  the  favorite  wood  for  struts  as  it  is  very  strong  along  the 
grain  in  tension  or  compression.  The  strength  of  steel,  weight  for 
weight,  would  have  to  be  180,000  ll)s.  per  scpiare  inch  to  ecpial  spruce  for 
this  purpose.  Spruce  is  not,  however,  very  strong  across  the  grain  and 
splits  readily,  hence  it  is  not  a  great  favorite  for  parts  subject  to  shearing 
or  cross-l)ending  stresses.  On  account  of  the  liability  of  spruce  to  split- 
ting, the  ends  of  the  struts  are  sometimes  encased  in  copper  ferrules  or 
bands.     This  prevents  crushing,  splitting  and  chafing. 

Compression  Struts 

When  a  member  is  subjected  to  a  compression  force  it  tends  to  bend 
or  buckle  in  the  center.  To  resist  this  tendency,  struts  subject  to  com- 
pression stress  are  umde  larger  in  the  center  than  at  the  ends. 

Ash  is  selected  for  the  longerons  because  it  is  strong  for  its  weight 
(about  38  lbs.  per  cu.  ft.),  very  elastic  and  can  be  obtained  in  long, 
straight-grained  pieces  free  from  defects.  It  is  strong  across  the  grain 
so  that  it  is  able  to  resist  the  compression  due  to  clips  and  struts  at- 
tached at  various  points  on  the  longerons. 

The  metal  clips  in  which  the  ends  of  the  struts  are  mounted  ase 
punched  from  sheet  steel  then  pressed  to  form.  They  are  frequently  nmde 
of  two  or  three  separate  pieces  which  are  then  electrically  spot-welded 
together.    They  are  made  of  .28  to  .30  percent  carbon  steel. 

The  lower  cr<)ss-meml)ers  of  the  fuselage  at  stations  3  and  4,  num- 
bered from  the  front,  terminate  in  a  half  hinge  to  which  the  lower  wing- 
sections  are  attached  on  either  side  of  the  fuselage.  These  cross-members 
serve  as  compression  members  when  a  machine  is  on  the  grcmnd,  but  when 
it  is  in  the  air  they  become  tension  members. 

Engine  Bearers 

The  engine  bearers  are  nmde  of  spruce  with  a  strip  of  ash  glued  on 
top  and  bottom.  They  are  further  protected  against  crushing,  at  points 
where  the  engine  supporting  arms  rest  on  the  sills  or  stringers,  by  melius 
of  a  copper  band. 

There  is  usually  a  fire  screen  between  the  engine  space  and  the  cock- 
pit. This  is  to  prevent  injury  to  the  pilot  so  far  as  possible  in  case  of 
a  back  fii'e  or  fire  in  the  engine  space. 


'1 


■  Ce^/ff/»-  /Sv7ff/ 


Fig.  31 — Hhomnij  principal  parts  of  fiisehi 


RIGGING  49 

Tlie  seat  rails  are  sliort  loiiiiitndinal  iiicniltcrs  forjiiiii^  siippoi-ts  for 
tlie  pilot's  and  observer's  seats.  These  rails,  which  are  mounted  on  either 
side  of  the  fuselage,  are  attached  to  adjacent  vertical  struts  at  the  proper 
distance  above  the  lower  longerons. 

The  rudder  bar  is  a  cross  bar  pivoted  at  its  center  and  mounted  a 
short  distance  above  the  floor  of  the  fuselage.  It  is  used  to  control  the 
vertical  rudder  and  is  operated  by  the  pilot's  feet.  Ordinarily  the  ends 
of  the  rudder  bar  project  through  the  sides  of  the  fuselage,  working  in 
suitable  slots  cut  for  them,  and  the  rudder  wires  are  attached  to  the 
ends  of  the  rudder  bar  outside  of  the  fuselage.  In  machines  fitted  with 
dual  controls  there  are,  of  course,  two  rudder  bars  and  these  are  fastened 
together  by  means  of  wires  connecting  their  outer  ends.  The  rear  of  the 
two  rudder  bars  is  then  connected  to  the  vertical  rudder  in  the  usual  way. 

Wing  section  struts  are  vertical  or  diagonal  struts  mounted  above 
the  fuselage  and  attached  b}^  means  of  strut  sockets  to  the  upper  longer- 
ons. The  wing  section  struts  are  used  to  support  the  center  wing  panel 
when  the  machine  is  on  the  ground  and  when  in  the  air  they  help  to 
support  the  fuselage  from  the  center  panel,  the  latter  being  supported 
partly  by  the  upper  wing  sections  which  are  attached  on  either  side  of 
it  and  partly  by  the  lower  wing  sections  which  are  braced  to  the  upper 
sections  and  also  attached  on  either  side  of  the  fuselage  as  previously 
described. 

The  strut  sockets  in  which  the  lower  ends  of  the  wing  section  struts 
are  mounted  consist  of  U-shaped  steel  plates  firmly  attached  to  the  upper 
longeron.  The  wing  section  struts  are  mounted  between  the  side  walls 
of  the  socket,  usually  by  means  of  a  heavy  through-bolt. 

Standard  Fuselage  Construction 

The  type  of  fuselage  just  described,  which  is  of  wood  and  metal  con- 
struction, may  be  said  to  represent  standard  practice  in  this  ccumtry 
at  the  present  time.  There  are,  however,  other  types  of  construction, 
such  as  the  all-steel  fuselage.  In  this  the  shape  of  the  members  and  the 
methods  of  joining  them  follow  closely  standard  methods  in  structural 
steel  work.  It  is  claimed  for  the  all  steel  construction  that  it  is  lighter 
for  a  given  size  machine  than  the  wood  and  metal  or  composite  con- 
struction. 

The  fuselage  is  usually  covered  either  with  canvas  or  linen  material 
similar  to  that  used  for  wing  coverings  or  else  with  very  thin  panels  of 
veneered  wood.  In  the  former  case  the  longerons,  struts  and  braces  must 
carry  all  the  weight  and  take  up  all  the  stresses  to  which  the  fuselage  is 
subjected,  but  when  a  veneered  wood  covering  is  used,  it  contributes 
materially  to  the  strength  of  the  fuselage,  consequently  the  framework  of 
the  latter  may  be  made  lighter. 

There  are  also  fuselages  of  the  monocoque  type  in  which  the  strength 
is  obtained  not  by  a  truss  construction,  but  by  the  form  and  nature  of  the 
outer  shell  itself,  this  being  made  up  of  alternate  layers  of  thin  wood 
veneering  and  cloth  until  the  desired  thickness  and  streugtii  are  obtained. 


50  APPLIED   AERONAUTICS 

The  various  layers  of  wood  veneering  are  laid  with  the  grain  running  in 
different  directions  in  the  different  layers.  This  type  of  shell  or  body, 
which  is  usually  somewhat  fish-shaped,  possesses  the  necessary  strength 
and  elasticity  without  the  system  of  struts  and  tie  wires  common  to  the 
ordinary  or  trussed  type  of  fuselage.  The  monocoque  construction  pos- 
sesses one  marked  disadvantage,  however,  and  that  is  that  it  is  veiy  hard 
to  repair  in  case  of  slight  damage. 

It  may  be  added  that  the  monocoque  or  laminated  wood  construction 
is  far  more  common  in  foreign  countries,  particularly  France  and  Ger- 
many, than  in  the  United  States. 

Landing  Gear 

The  landing  gear  is  an  assembly  of  struts,  fittings,  axle,  wheels, 
shock  absorbers  and  bracing  wires  whose  function  is  to  enable  the  ma- 
chine to  rise  from  and  land  on  the  ground  and  to  furnish  the  main  sup- 
port of  the  machine  when  resting  on  the  ground. 

The  struts  of  the  landing  gear  are  of  streamline  shape  to  reduce  the 
resistance  when  flying.  They  are  usually  made  of  well-seasoned, 
straight-grained  ash  or  sj>ruce.  Very  often  they  are  further  strength- 
ened by  several  Avrappings  of  linen  twine.  The  struts  with  their  fit- 
tings constitute  important  members  and  should  be  carefully  examined 
at  frequent  intervals.  Failure  or  collapse  of  these  struts  would  be  almost 
certain  to  cause  a  serious  accident  when  landing. 

These  struts  are  attached  to  the  lower  side  of  the  fuselage,  usually 
to  the  lower  longerons  themselves  by  means  of  metal  socket  fittings.  The 
lower  ends  of  the  struts  on  each  side  of  the  landing  gear  are  joined  to- 
gether by  a  metal  bridge.  This  bridge  not  only  serves  to  tie  the  lower 
ends  of  the  struts  together,  but  it  also  forms  a  yoke  or  housing  in  which 
the  axle  box  plays  up  and  down.  The  bridge  is  made  of  a  steel  stamping 
or  drop  forging. 

The  axle  box  may  be  in  the  form  of  a  whole  box  or  a  half  box.  When 
it  is  in  the  form  of  a  half  box  it  is  generally  called  a  saddle.  Its  purpose 
is  to  support  the  axle  and  to  guide  its  vertical  motion  in  the  bridge.  The 
saddle  may  be  either  of  bronze  or  aluminum.  It  is  held  in  its  place  in 
the  bridge  by  a  Avrapping  of  elastic  cord,  which  consists  of  a  number  of 
strands  or  bands  of  rubber  bunched  together  and  enclosed  in  a  loosely- 
braided  covering. 

The  assembly  of  the  saddle,  bridge  and  elastic  cords  is  called  the 
shock  absorber. 

The  axle  is  made  of  steel  tubing  and  is  enclosed,  between  the  bridges 
connecting  the  pairs  of  struts,  in  an  axle  casing.  This  is  made  of  wood, 
or  sheet  metal,  built  around  the  axle  itself  and  is  of  streamline  shape  or 
section  to  reduce  air  resistance. 

The  wheels  are  the  ordinary  type  of  wire  wheels  of  rather  small 
diameter  and  usually  fitted  with  pneumatic  tires.  They  do  not,  how- 
ever, ordinarily  run  on  ball  bearings,  as  a  slight  amount  of  friction  in 
the  wheel  bearings  is  of  little  or  no  conseciuence  Avhen  leaving  the  ground 


RIGGING  51 

at  the  eoinineueeiuoiil  of  a  flij;lit,  aud  it  assists  soiiicw  hat  in  briii^iiii^-  the 
machine  to  a  stop  without  going  too  far  after  aligliting.  The  sides  of  the 
wheels  are  covered  with  linen  cloth  discs  to  decrease  air  resistance. 

Not  all  landing  gears  are  like  the  one  described,  but  this  may  be 
taken  as  standard  practice.  Some  are  provided  with  a  skid  or  a  single 
wheel  projecting  ahead  of  and  above  the  main  wheels  for  the  purpose  of 
preventing  the  machine  from  taking  a  header  or  nosing  into  the  ground 
on  landing,  in  case  it  strikes  the  ground  at  too  sharp  an  angle.  Other 
minor  details  of  construction  will  be  noted,  too,  on  different  types  of 
nmchines,  particularly  in  the  construction  of  the  shock  absorbers. 

The  tail  skid  is  a  skid  or  arm  projecting  below  the  fuselage  near-  its 
rear  end.  The  purpose  of  the  tail  skid  is  twofold;  first,  to  support  the 
rear  end  of  the  airplane  when  on  the  ground  or  in  landing  and  prevent 
damage  to  the  rudder  and  elevators  and  their  controls,  and  secondly,  to 
act  as  a  drag  or  brake  to  assist  in  bringing  the  machine  to  a  stop  when 
landing.  The  tail  skid  is  frequently  hinged  or  pivoted  where  it  is  at- 
tached to  the  lower  longerons  and  its  upper  end,  extending  above  the 
pivotal  point,  fitted  with  rubber  cords  similar  to  those  used  in  the  shock 
absorbers  on  the  axle  of  the  landing  gear.  This  construction  acts  the 
same  way  as  the  shock  absorber  and  prevents  damage  to  the  empaunage 
and  rear  portion  of  the  fuselage  when  landing. 

Airplanes  are  often  fitted  with  wing  skids  which  consist  of  small 
auxiliary  skids  under  the  outer  ends  of  each  lower  wing.  These  skids 
ordinarih'  do  not  come  into  action  and  are  only  provided  to  prevent  dam- 
age to  the  outer  wings  in  alighting  on  rough  ground  or  in  case  a  sudden 
side  gust  of  wind  should  tend  to  upset  the  machine  when  alighting  or 
rising. 

Landing  Gear  of  Seaplanes 

Seaplanes  and  flying  boats  are  of  course  fitted  with  entirely  dif- 
ferent types  of  landing  gear  from  that  described.  Seaplanes  are  fitted 
with  pontoons  or  floats  suitable  for  arising  from  and  alighting  on  the 
water.  Usually  tliere  are  one  or  two  main  pontoons  under  the  forward 
section  of  the  fuselage,  these  corresponding  roughly  to  the  main  landing- 
gear  of  the  airplane.  There  is  also  a  smaller  pontoon  mounted  under  the 
rear  end  of  the  fuselage  and  one  under  the  outer  end  of  each  wing  to 
prevent  the  wings  dipping  or  the  whole  machine  upsetting  in  rough 
water.  The  flying  boat  is  so  constructed  that  the  whole  fuselage  is  in 
the  shape  of  a  boat  and  the  whole  macliine  is  therefore  supported  on 
tlie  fuselage  when  resting  on  the  water  and  when  alighting  and  rising 
from  the  water.  The  flying  boat  is  also  usually  fitted  with  small  auxil- 
iary pontoons  under  the  outer  end  of  the  wings  to  keep  the  machine 
steady  in  rough  water. 

The  main  members  running  the  full  length  of  the  wing  are  called 
the  spars.  They  are  usually  spoken  of  as  front  and  rear  spars.  Some- 
times the  front  spar  is  called  the  main  spar. 

The  cross  members  joining  the  spars  together  are  called  ribs.  There 
are  two  kinds  of  these,  compression  ribs  and  the  web  ribs.     The  function 


S2 


APPLIED   AERONAUTICS 


RIGGING  53 

vi  the  web  ribs  is  merely  to  siippoit  the  linen  covering  of  the  wings  and 
to  resist  the  lifting  force  of  the  air,  due  to  the  forward  motion  of  the  air- 
plane. 'I'here  is  not  much  end  pressure  against  these  ribs,  therefore,  the 
central  portion  is  cut  out  for  the  sake  of  lightening  them.  The  function 
of  the  compression  ribs  is  not  only  to  resist  the  lifting  force  of  the  air,  but 
also  to  take  the  thrust  due  to  the  stay  wires. 

The  ribs  are  not  continuous,  that  is,  they  do  not  pass  through 
the  spars.  The  ribs  are  made  in  three  sections,  the  nose  section,  center 
section  and  tail  section.  'J'he  nose  section  of  a  rib  is  the  section  which 
projects  for\\ard  of  the  front  or  main  spai*.  The  center  section  is  the 
section  between  the  front  and  rear  spars.  The  tail  section  of  the  rib  is 
that  which  projects  to  the  rear  of  the  rear  spar.  The  nose  sections  and 
tail  sections  are  sometimes  called  nose  ribs  and  tail  ribs  and  are  also 
frequently  spoken  of  as  nose  webs  and  tail  webs,  because  they  are  cut 
out  to  a  Aveb  form.  These  rib  sections  are  not,  of  course,  called  upon  to 
stand  compression  stresses,  as  these  stresses  are  all  centered  in  or  taken 
through  the  front  and  rear  spars. 

A  thin  strip  of  wood  running  from  the  nose  web  across  the  spars  to 
the  rear  end  of  the  tail  webs  (lengthwise  of  the  airplane  itself)  and 
serving  to  bind  all  the  wing  parts  or  ribs  together,  is  called  the  cap  strip. 
There  is  a  top  cap  strip  and  a  bottom  cap  strip  on  each  set  of  ribs. 

Entering  and  Trailing  Edges 

The  front  edge  of  the  wing  section  which  is  the  part  carrying  the 
nose  webs  or  nose  ribs  is  called  the  entering  edge  of  the  wing.  The  rear 
edge  of  the  wing  is  known  as  the  trailing  edge. 

The  nose  webs  are  tied  together  by  a  strip  of  spruce  running  full 
length  of  the  wing  or  crosswise  of  the  airplane  itself.  This  strip  forms 
the  leading  edge  of  the  wing  and  is  called  the  nose  strip.  From  the  nose 
strip  to  the  front  or  main  spar,  on  the  upper  side  of  the  wing,  there  is 
a  covering  of  thin  laminated  wood  colled  the  nose  covering.  Its  pur- 
pose is  to  reinforce  the  covering  fabric  as  it  is  at  this  point  that  the 
effect  of  wind  pressure  due  to  velocity  is  most  severe. 

t^econdary  nose  ribs  are  placed  between  each  pair  of  full  ribs  to 
give  additional  support  to  the  nose  covering. 

There  are  usually  two  rod-like  members  running  from  end  to  end  of 
the  wing  through  the  central  part  of  the  ribs.  These  are  called  stringers 
and  are  used  for  the  purpose  of  giving  lateral  stiffness  to  the  ribs. 

The  trailing  edge  of  the  Aviiig  is  made  of  thin  flattened  steel  tubing 
attached  to  the  tail  webs  by  metal  clips. 

The  spars  are  continuous  throughout  their  length.  Furthermore, 
they  have  reinforcements  of  wood  at  the  points  where  the  interplane 
struts  connecting  the  upper  and  lower  wings  are  attached.  Steel  bearing- 
plates  are  bolted  to  the  Aving  spars  at  these  points.  The  bolts  attaching 
these  bearing  plates  to  the  wing  spars  do  not  pass  through  the  spars 
themselves,  but  through  the  reinforcements.  This  is  to  avoid  weakening 
the  spars. 


54  APPLIED  AERONAUTICS 

Nearly  all  wood  used  in  wing  construction  is  spruce,  with  the  ex- 
ception of  the  nose  covering  which  is  made  of  birch  or  gum  wood,  the 
web  ribs,  which  are  made  of  laminated  wood,  and  small  quantities  of  pine 
or  other  woods  in  the  sidewalk  and  other  unimportant  places. 

The  sidewalk  is  a  boxed-in  or  wood-covered  portion  of  the  inner  end 
of  the  lower  wing.  It  furnishes  a  solid  footing  for  the  pilot  or  observer 
when  entering  or  leaving  the  cockpit  and  for  mechanics  working  around 
the  engine,  guns,  instruments,  control  mechanism,  etc. 

Steel  hinge  pieces  are  bolted  to  the  inner  ends  of  the  wing  spars 
and  serve  as  a  means  of  connecting  the  lower  wings  to  the  fuselage  and 
the  upper  wings  to  the  center  wing  panel. 

Interplane  struts  are  vertical  or  inclined  wooden  struts  of  stream- 
line section  used  to  transfer  compression  stresses  from  the  lower  wings 
to  the  upper  wings  when  the  machine  is  in  flight.  These  struts  are  used 
in  conjunction  with  diagonal  stay  wires  which  serve  to  transfer  the  load 
towards  the  center  of  the  machine  when  in  flight. 

The  stay  wires  are  divided  into  two  general  groups,  those  which  take 
the  drift  load  or  fore-and-aft  stresses  due  to  the  forward  motion  of  the 
airplane,  and  those  which  take  the  lift  load  or  vertical  load  due  to  the 
weight  of  the  machine  itself  and  the  vertical  resistance  when  in  the 
air.  The  lift  wires  are  again  divided  into  those  which  take  the  load  when 
the  machine  is  flying  and  those  which  take  it  when  on  the  ground.  The 
wires  which  take  the  lift  load  when  the  nuichine  is  in  the  air  are  called 
the  flying  wires,  and  those  which  take  the  load  when  on  the  ground  are 
called  ground  or  landing  wires. 

Drift  and  Anti-Drift  Wires 

The  set  of  wires  in  the  wings  which  carry  the  drift  load  when  flying- 
are  called  the  flying  drift  wires,  or  drift  wires  for  short.  There  is  no 
reversal  of  load  in  these  wires  when  the  machine  is  on  the  ground,  but 
opposition  wires  are  necessary  to  maintain  structural  symmetry.  These 
latter  are  called  the  anti-drift  wires. 

When  the  wing  frames  are  covered  it  is  of  course  impossible  to  in- 
spect the  internal  stay  wires  of  the  wings,  hence  every  precaution  must 
be  taken  to  guard  against  corrosion.  The  wire  used  at  this  point  is  tin 
coated  before  assembling,  the  steel  parts  of  the  turnbuckles  and  other 
fittings  are  copper  plated  and  when  completely  assembled,  all  the  metal 
parts  are  given  a  coat  of  enamel  paint.  All  screws,  tacks  and  brads  are 
of  brass  or  copper. 

Wings  are  covered  with  a  closely  woven  fabric.  At  present  un- 
bleached linen  seems  to  give  the  best  satisfaction.  Owing  to  its  scarcity, 
ho^^ever,  a  satisfactory  substitute  is  being  sought  for.  A  cloth  made  of 
long  fibre  sea  island  cotton  is  used  to  some  extent  and  makes  a  fairly 
satisfactory  substitute. 

Linen  fabric  weighs  3^  to  4f  oz.  per  sq.  yd.  and  has  a  strength 
of  GO  to  100  lbs.  per  in.  of  width.     Its  strength  is  increased  25  to  30 


RIGGING  55 

perceut  by  d(>i»iii;^,  liowevei'.  The  weight  of  cotton  faln'ie  iw  2  to  4  o/>.  per 
sq.  yd.,  its  strength  30  to  60  lbs.  per  in.  of  width,  and  its  strength  is  in- 
creased 20  to  25  jK'rceut  by  the  ap]tlicatioii  of  dojM'. 

The  cloth  surfaces  or  wing  coverings  nnist  be  taut,  otherwise  on  pass- 
ing through  the  air  they  would  vibrate  or  whip.  This  would  not  only 
increase  the  resistance  to  a  great  extent,  Itut  soon  would  lead  to  the  de- 
struction of  the  fabric.  A  preparation  called  dope  is  used  to  tighten 
up  the  fabric  and  give  a  smooth,  taut  surface.  It  also  tends  to  make  the 
cloth  weather-proof. 

Dope  should  be  easy  of  applicati(jn,  durable,  fire  resisting  and  have 
a  preserving  effect  on  the  cloth.  Dopes  at  present  are  divided  into  two 
classes  or  chemical  groups,  those  which  are  made  from  a  base  of  cellulose 
nitrate  or  pyroxylin  and  those  made  from  a  cellulose  acetate  base.  The 
base  is  dissolved  in  a  suitable  solvent,  such  as  acetone  for  instance,  and 
sometimes  other  substances  are  added  to  preserve  flexibility  or  prevent 
drying  out  and  cracking  and  checking  or  to  modify  shrinkage. 

The  greatest  difference  between  these  two  dopes  is  in  their  relative 
inflammability.  The  acetate  dope  makes  the  fabric  not  fireproof,  but 
slow  burning.  A  cloth  treated  with  this  dope  will  shrivel  and  char  l)efore 
burning,  but  one  treated  with  nitrate  do])e  will  burst  into  flame  immedi- 
ately on  the  application  of  a  lighted  match  or  when  exposed  to  a  strong 
spark  or  punctured  by  a  flaming  bullet,  etc.  See  "Airplane  Dopes,"  by 
Gustavus  J.  Esselen,  Jr.,  in  Aviation,  July  5,  1917. 

Inspection  windows  are  often  inserted  in  wing  sections  over  and 
under  certain  control  joints  where  the  latter  are  carried  inside  the  wing 
section  itself.  For  instance,  the  aileron  control  cables  are  frequently 
run  inside  the  lower  wing  sections  to  a  jJuUey  attached  to  the  front  or 
main  spar  opposite  the  middle  of  the  aileron,  the  cable  then  passing  down 
at  a  slight  angle  and  through  a  thimble  or  sleeve  in  the  lower  covering 
of  the  wing  section  to  the  point  \A'here  the  cable  is  attached  to  the  aileron 
control  mast.  With  this  construction  inspection  windows  would  be  set 
in  the  upper  and  lower  coverings  of  the  lower  wing  immediately  above 
and  below  the  pulley  ovjer  which  the  control  cable  passes.  The  inspec- 
tion windows  are  usually  of  celluloid  or  other  transparent  material 
firmly  sewn  into  the  wing  covering  material. 

Stay  Wires  and  Splices 

Stay  wires  and  cables  are  used  extensiveh^  in  airplane  construction. 
Much  of  the  safety  of  the  nmchine  and  pilot  depends  upon  the  quality  of 
the  material  in  the  stay  wires,  the  care  used  in  adjusting  them  and  on 
the  character  of  the  terminal  splices. 

Three  kinds  of  materials  are  used  for  stay  wires:  solid  or  aircraft 
wire,  stranded  wire  or  aircraft  strand,  and  a  number  of  strands  twisted 
together  to  form  a  cable  and  known  as  aircraft  cord.  Aircraft  wire  is  a 
hard  drawn  carbon  steel  wire  coated  with  tin  to  protect  it  against  cor- 
rosion. Its  strength  runs  from  200,000  to  .SOO.OOO  llis.  per  sq.  in., 
depending  upon  how  small  it  is  drawn.     Drawing  increases  both  the 


56 


APPLIED   AERONAUTICS 


strengtli  and  hardness  of  this  type  of  wire,  but  if  drawn  until  too  hard  it 
cannot  be  bent  with  safety.  The  aim  is  to  produce  a  wire  of  maximum 
strength,  yet  with  sufficient  toughness  to  allow  it  to  bend  without  frac- 
ture. A  standard  test  for  bending  is  to  grip  the  wire  in  a  vice  whose  jaAvs 
have  been  rounded  off  to  3/16  in.  radius,  and  bend  the  wire  back  and 
forth  through  an  angle  of  180  deg.  Each  bend  of  90  deg.  counts  as  one 
bend.  The  minimum  number  of  bends  for  various  sizes  of  aircraft  wires 
should  be  as  follows : 


For  wire  of  B. 
For  wire  of  B. 
For  wire  of  B. 
For  wire  of  B. 
For  wire  of  B. 
For  wire  of  B. 


&  S.  gauge  Xo.     6- 
&  S.  aauae  Xo.    8- 


5  bends  without  fracture. 
8  bends  without  fracture. 


&  S.  gauge  No.  10 — 11  bends  without  fracture. 
&  S.  gauge  No.  12 — 17  bends  without  fracture. 
&  S.  gauge  No.  11 — 25  bends  witliout  fracture. 
&  S.  gauge  No.  10 — 31  bends  without  fracture. 


Aircraft  strand  is  composed  of  a  number  of  small  wires,  usually  19, 
twisted  together.  The  individual  wires  of  the  strand  are  galvanized  or 
zinc  coated  before  being  twisted  into  the  strand.     The  complete  strand 


/s/. 


o 


13 


117 


2/?c/. 


3rd. 


4/k 


VX^ 


F'kj.  33 — ^tcps  ill  rnal'iiuj  an  cud  .splice  in  solid  icire 


is  more  flexible  than  a  solid  wire  of  the  same  diameter  and  is  therefore 
more  suitable  for  stay  wires  that  are  subject  to  vibration. 

The  stay  wires  of  the  fuselage  at  the  engine  and  wing  panels  are  of 
aircraft  strand  or  cord,  but  for  the  remaining  stay  wires  of  the  fuselage 
aircraft  Avire  is  ordinarily  used. 

Aircraft  cord  is  much  more  flexible  than  the  strand.  It  is  used 
for  control  cables  where  these  must  pass  over  comparatively  small  pul- 


RIGGING  57 

leys.  Tlie  usual  iMdistnutiou  of  niiTi-alt  cord  is  7  strands  of  I'J  wires 
each  tAvisted  together  to  form  a  cable.  This  specification  is  known  as 
7  X  10  aircraft  cord.  The  individual  wires  of  the  cord  are  very  small  and 
are  tin-plated  before  being  stranded. 

For  a  given  diameter,  the  solid  wire  is  stronger  than  either  the 
strand  or  cord.  Weight  f(»i-  weight,  however,  the  cord  is  a  little  stronger 
than  the  wire,  as  shown  l»y  the  following  tabh'. 

Weight  Strength  for  a  Strength  for  a 

per  100  ft.  given  diameter  given  weight 

Wire                           8.84  lbs.                 5500  lbs.  5500  lbs. 

(;ord                             0.47  lbs.                  4200  lbs.  5000  11)S. 

A  wire  or  cord  is  no  stronger  than  its  terminal  splice.  The  splice 
may  be  formed  in  a  variety  of  ways.  For  solid  wire  the  formation  of 
the  eye  is  important.  An  eye  in  which  the  reverse  curve  has  the  same 
radius  as  the  eye  proper  is  called  a  perfect  eye  and  is  the  one  recom- 
mended. The  inside  diameter  of  the  eye  should  be  about  three  times  the 
diameter  of  the  wire  itself. 

After  the  eye  is  formed  a  flattened  wrapped  wire  ferrule,  somewhat 
like  a  coiled  spring  flattened  to  eliptical  section,  is  slipped  over  the  wire 
and  the  free  end.  The  latter  is  then  bent  back  over  the  ferrule.  Such  a 
terminal  will  have  an  efficiency  of  60  to  05  percent  of  the  strength  of 
the  Avire  itself.  When  this  tyjte  of  terminal  fails  it  is  usually  by  slipping. 
If  the  free  end  of  the  wire  is  tied  doAvn,  after  being  bent  back  over  the 
ferrule,  with  an  additional  wrapping  of  wire,  the  efficiency  of  the  termi- 
nal as  a  whole  will  be  increased  to  80  percent  of  the  strength  of  the 
wire.  If  the  whole  terminal  is  soldered  the  efficiency  will  be  increased 
to  100  percent  according  to  static  tests.  This  is  misleading,  however,  as 
such  tests  take  no  account  of  live  load  stresses  or  vibration. 

Another  form  of  terminal  is  made  by  substituting  a  thin  metal  fer- 
rule or  section  of  flattened  tul)e  for  the  wrapped  wire  ferrule.  It  can  be 
made  secure  either  by  soldering  or  twisting  after  being  put  in  place.  This 
terminal  for  live  or  vibrational  loads  is  superior  to  the  wrapped  wire 
terminal  as  there  is  not  so  much  difference  in  mass  between  the  wire  and 
the  ferrule. 

Aircraft  Strand  Terminals 

The  terminal  eye  of  the  aircraft  strand  is  formed  around  a  thimble. 
The  free  end  of  the  strand  is  In-ought  around  the  thimble  and  either 
wrapped  to  the  main  strand  with  small  wires  and  soldered,  or  the  free 
end  is  spliced  into  the  main  strand.  Before  bending  around  the  thimble, 
the  strand  is  wrapped  with  fine  wire  in  order  to  prevent  flattening  oi- 
caging  of  the  strand. 

The  terminal  eye  of  the  airci'aft  cord  is  always  made  by  splicing  the 
free  end  of  the  cord  into  the  main  strands  after  wrap]iing  the  cord  around 
a  thimble.     Sometimes  the  splice  is  soldered  but  more  often  it  is  wrapped 


58  APPLIED  AERONAUTICS 

with  harness  twine.  Foreign  engineers  are  opposed  to  soldering,  claim- 
ing that  the  disadvantages  in  the  way  of  corrosion  and  overheating  of 
the  wire  outweigh  the  advantages  of  the  stronger  terminals. 

The  theory  of  the  splice  is  simple.  A  strand  or  wire  of  the  free  end 
is  wrapped  around  a  strand  or  wire  of  the  main  cord,  care  being  taken 
to  have  the  lay  of  the  wires  the  same.  Three  to  five  complete  turns  are 
given,  three  for  the  first  and  four  to  five  for  the  last  weaves  of  the  splice 
in  order  to  taper  the  splice  gradually. 

Objections  to  soldering. — The  most  serious  objections  to  soldering 
are :  a.  overheating ;  b.  corrosive  action  of  fluxes.  It  is  very  easy  to  over- 
heat and  soften  the  wire  and  this  is  all  the  more  serious  because  the 
softening  takes  place  at  a  point  where  the  wire  is  enlarged  by  the  joint. 
The  stress  is  naturally  localized  at  this  point. 

Some  of  the  so-called  non-corrosive  fluxes  will  upon  application  be 
found  to  be  more  or  less  corrosive.  Even  with  strictly  non-corrosive 
fluxes,  there  is  a  carbonaceous  residue,  due  to  heat,  driven  into  the  inter- 
stices between  the  wires  of  strands  or  cords.  This  serves  as  a  holder  for 
moisture  and  will  in  time  cause  corrosion. 

The  corrosive  effects  of  acid  fluxes  can  be  neutralized  by  the  appli- 
cation of  an  alkaline  solution,  such  as  soda  water.  Washing  the  soldered 
splice  of  a  solid  wire  with  such  a  solution  is  very  effective,  but  with 
strands  and  cords,  where  the  acid  is  driven  into  the  interior  through  the 
application  of  heat,  it  is  questionable  whether  any  system  of  washing 
will  eliminate  or  neutralize  the  acid.  Corrosion  of  the  interior  wires  of 
a  strand  or  cord  may  be  concealed  by  a  perfectly  good  exterior,  giving 
an  entirely  false  appearance  of  security. 

Turnbuckles 

Turnbuckles  are  made  of  three  parts,  the  ferrule  or  sleeve,  and  the 
two  ends.  To  distinguish  the  ends,  they  are  called  the  yoke  and  eye  ends, 
or  the  male  and  female. 

Great  care  should  be  exercised  when  tightening  or  loosening 
turnbuckles  that  the  cables  are  not  untwisted  or  frayed.  If  the  cables 
are  untwisted  a  caging  of  the  strands  results  which  greatly  weakens 
the  cable.  Cable  that  has  been  caged  should  be  replaced.  No  pliers 
should  be  used  when  tightening  or  loosening  turnbuckles.  The  correct 
method  is  to  use  two  drift  pins  or  nails,  one  through  the  terminal  eye 
of  the  cable  to  prevent  the  end  of  the  cable  twisting,  the  other  through 
the  hole  in  the  barrel  of  the  turnbuckle.  Pliers  will  scar  the  wires, 
which  is  objectionable  for  three  reasons,  the  first  two  of  which  may  lead 
to  serious  consequences.  These  reasons  are :  First,  breaking  the  pro- 
tective coating  given  to  guard  against  corrosion.  Second,  a  nick  or  scar 
in  a  wire  or  cable  which  would  weaken  it  considerably.  The  wire  or  cable 
may  not  show  much  reduction  of  strength  under  a  static  load  or  test,  but 
with  a  live  or  vibrational  load  the  strength  is  greatlv  reduced  and  a 


RIGGING  59 

slight  nick  will  determine  the  point  of  fracture.  Third,  disfiguration  of 
the  parts  is  offensive  to  the  eye  and  bespeaks  slouchy  or  careless  work- 
manship. 

Locking  Devices 

A  fair  proportion  of  accidents  occurs  to  moving  mechanism  through 
nuts  or  other  tlireaded  fastenings  working  loose.  It  is  safe  to  say  that 
several  hundred  patents  have  been  taken  out  for  nut-locking  devices,  but 
of  this  great  number,  a  few  only  are  of  practical  value  and  used  to  any 
extent.  The  castellated  nut  and  cotter  pin  used  of  course  with  a  drilled 
bolt  or  stud  is  one  of  the  few  devices  that  finds  large  application.  It  is 
generally  used  in  automobile  and  airplane  work.  The  spring  locking 
washer  is  another  good  device.  This  is  used  where  the  fastening  is  of  a 
permanent  or  semi-permanent  character.  Another  method  is  to  batter 
or  hammer  down  the  end  of  a  bolt  a  little.  This  should  be  practiced  only 
as  a  last  resort  or  as  an  absolutely  permanent  job  and  must  be  carefully 
done,  otherwise  serious  damage  will  result  to  the  bolt  and  nut.  It  is  suf- 
ficient to  close  one  thread  on  the  bolt  for  part  of  the  circumference  only. 

Turnbuckles  are  secured  against  turning  or  loosening  by  running 
a  wire  through  the  adjusting  hole  in  the  turnbuckle  sleeve  and  carrying 
the  vdre  back  and  binding  it  around  the  ends  of  the  turnbuckle.  See 
Fig.  41. 


Chapter  5 

ALIGNMENT 

Fuselage  alignment — Horizontal  and  vertical  stabilizers — Landing  gear  or  under-carriage 
— Center  wing  section — Wings — Lateral  dihedral  angle — Table  for  lateral  dihedral 
— Stagger — Overhang — Rigger's  angle  of  incidence — Wash-out  and  wash-in — Over- 
all measurements — Aileron  controls — Elevator  controls — Rudder  control — Notes  on 
aligning  boards. 

BY  the  term  airplaue  aligmneut  is  meaut  the  art  of  triiiug  up  an  air- 
plane, and  adjusting  the  parts  in  their  proper  relation  to  each  other 
as  designated  in  the  airplane's  specifications.  The  inherent  stability,  the 
speed,  the  rate  of  climb,  the  efficiency,  in  short  the  air\yorthiness  of  an 
aircraft  depend  in  large  measni'e  on  its  correct  alignment.  For  this 
reason  the  importance  of  careful  and  correct  alignment  cannot  be  oyer- 
estimated. 

The  instructions  as  giyen  in  this  chapter  are  not  intended  to  lie  a 
comiDlete  and  exhaustiye  treatise  on  the  Ayhole  subject  of  airplane  align- 
ment, but  are  designed  rather  to  giye  the  beginner  a.  good  general  idea 
of  how  the  work  is  done.  Thus  with  these  instructions  as  a  ground  work 
he  can  become  proficient  in  the  work  after  having  had  good  practical 
experience  in  the  hangars. 

The  work  of  aligning  an  airplane  divides  naturally  into  several  dis- 
tinct and  separate  groups  or  divisions — a.  fuselage,  b.  horizontal  and 
vertical  stabilizers,  c.  landing  gear,  d.  center  wing  section,  e.  wings,  f. 
controls. 

Alif/iiiitent  of  fiischuje. — The  fuselage  is  aligned  before  leaving  the 
airplane  factory  and  normally  this  alignment  will  last  for  some  time. 
Tlie  fuselage  alignment  should  be  checked  over  carefully,  however,  after 
an  airplane  has  been  shipped  in  disassembled  condition.  Strains  on  the 
fuselage  caused  by  rough  handling,  bad  landings,  etc.,  will  make  it  nec- 
essary to  re-align  it. 

Before  attempting  to  align  any  part  of  an  airplane  the  erection  draw- 
ings should  be  referred  to  if  available,  and  the  directions  furnished  by 
the  makers  should  be  followed  carefully  unless  the  operator  has  had  a 
great  deal  of  previous  experience  upon  the  particular  type  of  airplane  to 
be  aligned,  and  is  familiar  with  better  methods  of  procedure  than  those 
recommended  bv  the  maker. 


ALIGNMENT  61 

In  general  the  procedni'e  in  aligning  a  fuselage  will  lie  about  as  fol- 
lows: A  horizontal  reference  plane  is  nsnally  specified  by  the  makers  in 
connection  with  the  fuselage.  Sometiuies  the  top  longerons  are  taken 
as  this  reference  plane,  in  which  case  they  are  to  be  aligned  horizontally, 
laterally,  and  longitudinally  from  a  specified  station  to  the  tail  post. 
Sometimes  horizontal  lines  are  drawn  on  the  vertical  fuselage  struts,  and 
the  fuselage  is  so  aligned  that  these  lines  all  fall  in  the  same  horizontal 
plane. 

Alignment  of  Longerons 

In  the  first  case,  after  the  fuselage  has  been  placed  in  a  flying  posi- 
tion, the  top  longerons  are  aligned  for  straightness,  using  a  straight  edge 
and  a  spirit  level  to  aid  in  finally  placing  them  laterally  and  longitudi- 
nally in  a  liorizontal  plane. 

The  longerons  are  next  aligned  symmetrically  with  respect  to  the 
imaginai'y  vertical  plane  of  symmetry  through  the  fore-and-aft  axis  of 
the  fuselage.     There  are  two  general  methods  of  doing  this,  as  follows : 

First  Method — The  center  points  are  mai'ked  on  all  horizontal 
fuselage  struts.  A  small,  stout  cord  is  stretched  from  the  center  of  the 
fuselage  nose  to  the  tail  post  and  the  horizontal  bracing  wires  adjusted 
until  the  centers  of  the  horizontal  struts  fall  beneath  this  line.  A  small 
surveyor's  plumb  bob  is  held  at  different  points  so  that  the  suspending 
cord  just  touches  the  fore-and-aft  aligning  cord.  The  centers  of  the 
bottom  horizontal  struts  should  fall  directly  below  the  bob. 

Second  Method — A  plumb  line  is  dropped  from  the  center  of  the 
propeller  and  from  the  tail  post  and  a  string  is  stretched  on  the  ground 
or  floor  between  these  two  points.  Plumb  bobs  dropped  from  the  centers 
of  the  horizontal  struts  must  point  to  this  line. 

The  whole  fuselage  alignment  is  checked  to  make  sure  that  it  agrees 
with  the  specifications.  If  the  airplane  has  a  nou-liftiug  tail,  it  would 
be  advisable  as  the  next  step  to  support  the  fuselage  in  such  a  way  that 
the  rear  part  (about  two-thirds  of  the  total  fuselage  length)  remains  un- 
supported, and  then  re-check  tlie  fuselage  alignment  once  more. 

All  turnbuckles  should  then  be  securely  locked  and  the  fuselage 
carefully  inspected. 

Horizontal  and  Vertical  Stabilizers 

The  vertical  stabilizer  is  examined  to  see  that  tlie  bolts  holding  it  in 
place  are  properly  drilled  and  cotter-pinned,  also  to  see  that  it  is  set 
parallel  or  dead  on  to  the  direction  of  motion.  It  is  trued  up  vertically 
by  the  turnbuckles  on  the  tie  wires  or  brace  wires  connected  to  it.  These 
turnbuckles  are  then  properly  safetied. 

The  horizontal  stabilizer  usually  is  braced  with  tie  wires  fitted  with 
turnbuckles.  By  means  of  these  its  trailing  edge  should  be  made  straight 
and  at  right  angles  to  the  horizontal  center  line  of  the  fuselage.  All 
bolts  fastening  the  horizontal  stabilizer  to  the  fuselage  should  be  in- 
spected to  make  sure  they  are  properly  drilled  and  cotter-pinned.  All 
turnbuckles  should  be  safetied,  as  shown  iu  Fig.  41. 


62  APPLIED  AERONAUTICS 

Alignment  of  laiidiiuj  gear  or  under-carriage. — In  assembling  an 
airplane  which  has  been  completely  dismantled,  the  landing  gear  should 
be  assembled  to  the  fuselage  and  aligned  with  it  before  the  wings 
are  attached.  In  assembling  and  aligning  the  landing  gear,  the  fuselage 
should  be  so  supported  that  the  landing  gear  hangs  free  and  the  wheels 
do  not  touch  the  ground. 

The  fuselage  is  placed  in  the  flying  position,  or  at  least  in  such  a 
position  that  the  lateral  axis  is  horizontal.  There  are  three  general 
methods  of  aligning  the  landing  gear,  as  follows : 

First  Method — A  small  plumb  bob  is  dropped  from  a  point  on  the 
fore-and-aft  center  line  of  the  fuselage  above  the  axle  of  the  landing  gear. 
A  tack  is  placed  in  the  exact  center  of  the  axle  casing  or  a  scratch  is  made 
on  the  axle  at  its  center.  The  transverse  tie  wires  are  then  adjusted  until 
the  tack  or  center  line  mark  falls  exactly  below  the  plumb  bob.  The  wires 
are  made  moderately  tight.  The  exact  degree  of  tautness  required  can- 
not very  well  be  described;  it  is  a  matter  of  experience  or  personal  in- 
struction. All  turnbuckles  are  safetied  and  the  landing  gear  inspected 
carefully.  The  strut  fittings  and  the  elastic  shock  absorbers  should  be 
inspected  very  carefully. 

Second  IMethod — The  two  forward  transverse  tie  wires  are  adjusted 
until  equal  in  leng^th,  then  the  rear  transverse  tie  wires  are  similarly 
adjusted  until  they  also  are  equal  in  length.  All  transverse  tie  wires  are 
tightened  equally  and  the  turnbuckles  safetied.  The  landing  gear  is 
then  given  a  final  inspection. 

Third  Method — The  transverse  tie  wires  are  adjusted  until  the  axle 
is  horizontal  as  shown  by  a  spirit  level.  This  adjustment  is  made  with 
the  fuselage  in  the  flying  position  or  with  the  lateral  axis  horizontal. 
The  transverse  tie  wires  are  tightened  equally  to  the  correct  tautness,  the 
turnbuckles  safetied,  and  the  landing  gear  inspected  as  before. 

Center  Wing  Section 

Alignment  of  center  luing  section. — The  fuselage  is  first  placed  in 
the  flying  position,  and  the  center  wing  section  adjusted  symmetrically 
about  the  fore-and-aft  center  line  of  the  fuselage  in  plan.  A  tack  driven 
in  the  middle  of  the  leading  edge  of  the  center  panel  will  then  be  directly 
above  the  center  line  of  the  fuselage.  This  is  tested  with  a  small  plumb 
bob  and  checked  by  measuring  each  pair  of  transverse  tie  wires  to  see  if 
the  two  wires  of  each  pair  are  equal  in  length. 

The  alignment  for  stagger  is  made  by  adjusting  the  stagger  or  drift 
wires  in  the  fore-and-aft  direction  until  the  leading  edge  of  the  center 
panel  projects  the  required  distance  ahead  of  the  leading  edge  of  the 
lower  plane  as  given  in  the  airplane  specifications.  This  align- 
ment is  checked  by  dropping  a  plumb  bob  from  the  leading  edge  of  the 
center  panel  and  measuring  forward  in  a  horizontal  plane  from  the  lead- 
ing edge  of  the  lower  plane  to  the  plumb  line.  The  adjustment  for  stag- 
ger fixes  the  rigger's  angle  of  incidence.  All  turnbuckles  are  safetied 
and  the  alignment  re-checked. 


ALIGNMENT  63 

Aliy II incut  of  icings. — Before  any  attempt  is  made  to  align  the  wings 
the  fuselage  should  be  carefully  inspected  to  make  sure  that  it  is  properly 
rigged  and  in  proper  alignment.  Failure  to  do  this  ma}'  cause  much 
delay  and  waste  ot  time  in  aligning  the  wings. 

The  next  step  is  to  make  a  general  inspection  of  the  wings,  noting 
if  all  bolts  and  clevis  pins  are  properly  cotter-pinned.  Note  particularly 
the  clevis  pins  where  the  interplane  brace  wires  are  fastened  to  the  upper 
plane  fittings.  One  of  the  largest  airplane  makers  in  this  country  puts 
these  clevis  pins  in  head  down.  In  this  position  if  the  pins  are  not  prop- 
erly cottered,  there  is  great  danger  of  their  working  loose  and  dropping 
out,  disconnecting  the  wires.  Such  matters  are  more  easily  remedied 
before  the  wings  are  aligned  than  afterwards. 

Loosen  all  wires  between  the  planes  including  flying  wires,  ground 
wires,  stagger  wires  and  external  drift  wires.  Examine  the  turnbuckles  to 
see  that  the  same  number  of  threads  show  at  both  ends.  If  not,  take  the 
turnbuckle  apart  and  remedy  this.  It  will  mean  a  saving  of  time  in  the 
end  if  these  matters  are  looked  after  before  the  actual  truing  up  of  the 
wings  is  begun. 

Flying  Position 

Place  the  fuselage  in  the  flying  position  as  defined  in  the  airplane's 
erection  drawings.  This  may  mean  aligning  the  top  longerons  or  the 
engine  bed  or  other  specified  parts  laterally  and  longitudinally  horizon- 
tal. This  must  be  done  carefull}',  using  a  good  spirit  level,  because  the 
wings  are  aligned  from  the  fuselage  upon  the  assumption  that  this  flj^ing 
position  is  correct.  If  it  is  necessary  to  get  into  the  cockpit  or  in  any 
other  way  disturb  the  fuselage  during  the  alignment  of  the  wings,  make 
sure  that  the  fuselage  is  still  in  the  correct  flying  position  before  pro- 
ceeding further. 

Lateral  dihedral  angle. — There  are  thi'ee  common  methods  of  ad- 
justing for  lateral  dihedral : 

Aligning  Board 

First  Method — Aligning  Board.*  If  an  aligning  board  is  available 
its  use  saves  considerable  time  due  to  the  fact  that  the  rigger  secures 
the  lateral  dihedral  angle,  straightness  of  wing  spars,  and  correct  angle 
of  incidence  near  the  wing  tips  all  at  the  same  time.  The  protractor  level 
should  read  directly  in  degrees.  Set  this  instrument  at  the  number  of 
degrees  dihedral  stated  in  the  airplane's  specifications.  Place  the  align- 
ing board  parallel  to  the  front  spar  (by  measuring  back  from  the  strut 
fittings)  and,  keeping  the  flying  and  stagger  wires  loose,  pull  up  on  the 
ground  wires  until  the  bubble  on  the  protractor  level  reads  almost  level. 
Since  the  aligning  board  is  a  straight  edge  it  is  easy  to  keep  the  front  spar 
perfectly  straight  by  glancing  beneath  the  aligning  board  occasionally. 
It  should  rest  on  at  least  three  ribs,  one  near  each  end  and  one  near  the 
middle.  The  space  between  the  other  ribs  and  the  aligning  board  should 
be  slicrht. 


*See  note  on  aligning  boards  at  end  of  this  chapter. 


64 


APPLIED   AERONAUTICS 


Spiht  Lei/el 


Dihedral  Board 


F'kj.  34 — Metliod  of  ni<in<i  short  dllietlnd  hoard 

Place  the  aliiiniDg  board  in  front  of  and  parallel  to  the  rear  spar. 
Adjust  the  ground  wires  until  the  rear  spar  is  straight  and  the  dihedral 
is  slightly  greater  than  called  for  in  the  maker's  specifications.  Check 
at  the  front  spar.    It  will  now  be  the  same  as  the  rear.    If  not  make  it  so. 

Now  tighten  down  on  all  flying  wires  except  those  to  the  overhang, 
if  there  is  overhang.  Test  each  pair  of  flying  wires  for  equal  tautness 
by  striking  with  the  edge  of  the  hand  and  watching  their  vibration. 
The  loose  wire  has  the  greatest  amplitude  of  vibration.  The  lateral 
<lihedral  should  now  be  exactly  as  called  for  in  the  specifications. 

After  aligning  both  wings  for  dihedral  as  stated  above,  both  wings 
will  be  the  same  height  if  the  fuselage  is  level  laterally.  Check  the  height 
of  the  wings  by  making  the  distance  BA  (see  Fig.  35)  equal  to  DC  meas- 
ured from  the  longerons  opposite  the  butt  ends  of  the  front  spars  on  the 
lower  wing  panels.    V  is  a  tack  in  the  middle  of  the  leading  edge  of  the 


F'kj.  35 — Points  of  measurement  for   icing  alignment 


ALIGNMENT 


65 


center  section  panel.  ^Vitll  a  steel  tape  measure  the  distance  VA  and  VC. 
These  distances  slioiikl  be  equal. 

Equally  good  results  ma^'  be  obtained  by  using-  a  protract<jr  spirit 
level  in  conjunction  with  an  accurate  straight  edge. 

Second  ^letliod — If  a  good  aligning  board  is  not  available  the  string 
method  may  be  used.  Fig.  3(1  sliows  the  arrangement  of  the  string  which 
should  be  small,  smooth  and  tightly  drawn. 

Keep  the  stagger  wires,  flying  Avires  and  nose  drift  wires  loose  as  in 
the  first  method.  Increase  the  dihedral  angle  by  tightening  the  ground 
wires,  keeping  the  panels  straight  by  sighting.  The  greater  the  dihedral 
angle  the  greater  the  distance  Y  (see  Fig.  36).  The  tal)le  below  shows 
the  variation  for  customarv  range  of  lateral  dihedral : 


^ 


Sfn'njf 


string 


Mast   W/'re- 


'^^ 


rfc^ 


F'lfj.  ^6~AIteruatirc  method  of  aligning  for  dihedral 

Table  for  Lateral  Dihedral  Angles 


X 

Y 

Inches  Distance  from 

Inches  Distance  from 

Degrees 

point  of  support  of  string 

end  of  spar  vertically  up 

to  end  of  spar. 

to  the  horizontal  string. 

0 

100 

0 

1 

100 

1% 

2 

100 

3V2 

3 

100 

sy* 

4 

100 

7 

5 

100 

m 

6 

100 

lO/iT 

7 

100 

12^^ 

8 

100 

13ii 

3 

100 

15% 

10 

100 

17% 

66 


APPLIED   AERONAUTICS 


The  distance  X  will  probably  not  be  exactly  100  in.  as  given  in  the 
table,  but  since  X  and  Y  increase  in  the  same  proportion  this  is  very 
simple.  For  example,  the  distance  X  (convenient  to  measure)  on  a  bi- 
plane having  a  3  deg.  lateral  dihedral  angle  may  be,  say  12  ft.  6  in.,  or 
150  in.,  which  is  one  and  one-half  times  100  in. 

The  table  gives  Y  equal  to  5^  in.  for  3  deg.  Our  X  is  one  and  one- 
half  times  the  X  in  the  table.  Then  our  Y  must  be  one  and  one-half  times 
5^  in.  (the  Y  given  in  the  table),  which  equals  7^  in.,  which  is  the  proper 
distance  up  to  the  string  when  the  wing  has  the  correct  lateral  dihedral. 

In  determining  the  distance  Y,  always  measure  the  vertical  distance 
up  to  the  string  from  near  the  inner  edge  of  the  wing  panel,  not  from  the 
center  section  panel.  The  correct  lateral  dihedral  angle  having  been 
obtained-  proceed  further  as  in  the  first  method. 

Third  Method — On  airplanes  having  sweep-back  the  string  method 
is  rather  difficult  to  apply.  If  an  aligning  board  such  as  used  in  the  first 
method  is  not  available,  then  a  short  dihedral  board  may  be  made  wihich 
will  serve.     Fig.  37  shows  the  construction  and  Fig.  34  the  method  of 


Hhort  dihedral  hoard 


using  such  a  board.  It  is  plain  that  a  separate  board  must  be  made  for 
each  airplane  having  a  different  dihedral  from  the  others  at  a  flying 
field.  Another  disadvantage  of  this  board  is  the  fact  that  it  must  be  used 
between  struts  on  the  spars  and  is  so  short  that  it  is  apt  to  be  affected 
greatly  by  unequal  rib  heights  and  any  lack  of  straightness  in  the  spars. 

After  obtaining  the  correct  dihedral  proceed  as  in  the  first  method. 

Stagger  is  usually  given  in  airplane  specifications  as  a  linear  meas- 
urement in  inches.  The  specifications  will  tell  whether  it  is  to  be  meas- 
ured on  a  projection  of  the  chord  or  as  a  horizontal  distance.  (See 
Fig.  38.)     It  is  important  to  measure  the  stagger  in  the  manner  directed. 

The  stagger  of  the  wings  is  fixed  at  the  fuselage  by  the  stagger  of  the 
center  wing  section.  Align  for  stagger  by  adjusting  the  stagger  wires 
between  interplane  struts.  Slight  adjustments  only  should  be  necessary. 
Fig.  38  shows  the  method. 

In  exceptional  cases  the  flying  and  ground  wires,  front  and  rear, 
nearest  the  fuselage,  are  used  in  adjusting  the  stagger,  which  is  usually 
found  to  be  correct  however  after  slight  adjustments  of  the  stagger  wires. 


ALIGNMENT 


67 


Stagger  is  sometimes  given  as  an  angle  of  stagger  in  degrees.  This 
can  be  converted  into  inches  by  the  use  of  the  lateral  dihedral  table  on 
page  65.  In  this  case  AB  in  Fig.  38  corresponds  to  X  in  the  table,  and  Y 
in  Fig.  38  will  be  proportional  to  Y  in  the  table.  For  instance  if  AB  in 
Fig.  38  is  50  in.  in  a  given  airplane,  or  one-half  of  X  in  the  table,  and  the 
stagger  is  given  in  the  airplane's  specifications  as  7  deg.,  then  the 
amount  of  stagger  Y  (Fig.  38)  would  be  one-half  of  the  12  ^/jg  in.  given 
in  column  Y  in  the  table  opposite  7  deg. 

Overhang. — If  an  airplane  has  much  overhang  it  is  usually  supported 
by  mast  wires  above  and  flying  wires  below.  See  that  the  flying  wires 
are  loose.     Tightening  one  set  of  wires  against  an  opposing  set  throws 


Ang/e  ojT 


\ 


C  or  H  {k^/j/c/iet/ef  method  of  measuring 
the   specf/tcof/oiis  Co//  fofj  is  /he  ^fo^geK 


Fig.  38 — Methods  of  measuring  stagger 

undue  stress  in  members.  Tighten  up  on  the  mast  wires  until  the  over- 
hang inclines  very  slightly  upward.  Now  tighten  up  on  the  flying  wires 
below  until  the  spars  are  straight. 

The  leading  and  trailing  edges  of  all  wing  panels  should  now  be 
straight.  In  case  there  should  be  small  local  bows  in  the  spars,  with  a 
little  careful  adjusting  of  wires  these  can  usually  be  distributed  equally 
between  the  upper  and  lower  wing  panels  so  that  their  effect  will  be  les- 
sened. Fixing  the  lateral  dihedral  or  the  angle  of  incidence  for  either 
upper  or  lower  plane  automatically  adjusts  it  for  the  other  plane. 

Rigger's  angle  of  incidence. — Check  the  lateral  dihedral  to  make  sure 
that  it  has  not  been  altered  in  making  other  adjustments.     If  it  is  cor- 


68 


APPLIED   AERONAUTICS 


Spirit  Level 


A        B 


Sfraiyht   £</ye 


Fig.  39 — Measuring  angle  of  incidence  icith  straight-edge  and  spirit  level 

rect,  front  and  rear,  and  the  spars  are  straight,  then  the  angle  of  inci- 
dence should  be  correct  all  along  the  wing.  Figs.  39  and  40  show  two 
methods  of  testing  this.  If  the  set  measurements  A  or  B  are  known, 
the  first  method  (Fig.  39)  can  be  used.  If  the  angle  AOB  is  given  in  the 
specifications  then  the  second  method  (Fig.  40)  can  be  employed.  Test 
the  angle  of  incidence  near  the  fuselage  and  beneath  the  interplane  struts. 
Wash-out  and  toash-in. — Due  to  the  reaction  from  the  torque  of  the 
propeller  the  airplane  tends  to  rotate  about  its  longitudinal  axis.  To 
counteract  this  the  wing  which  tends  to  go  down  (sometimes  referred  to 
as  the  "heavy"  wing)  is  drawn  down  slightly  at  its  trailing  edge  towards 
its  outer  end,  or  in  other  words  it  is  given  a  slight  additional  droop  at  this 
point.  This  is  usually  referred  to  as  a  "wash-in."  The  wing  on  the 
other  side  of  the  machine  is  given  a  slight  upward  twist,  or  "wash-out" 
at  a  corresponding  point.     In  single-engined,  right-hand  tractors  wash- 


ySptrif  Level  ^Oe^rees 

' ^   yaafBoorJ  L 


straight  Ed^e 

Fig.  40 — Another  method  of  measuring  angle  of  incidence.  It  can  also 
be  done  advantageouslg  by  vsing  a  straight  edge  in  conjunction  with 
a  protractor  spirit  level 


ALIGNMENT 


69 


in  is  given  to  tlie  left  Avini>  ;nnl  Avash-ont  to  tlie  riulit.  To  increase  the 
angle  of  incidence  the  rear  spar  must  be  warped  down  hv  slackening  all 
the  wires  connected  to  the  bottom  of  the  strut  and  tightening  all  which 
are  connected  to  the  toj)  of  the  struts,  until  the  desired  amount  of  wash- 
in  is  secured.    This  process  is  reversed  to  secure  wash-out. 

For  purposes  of  increased  stability  wash-out  is  sometimes  given  both 
wings  although  of  course  some  lift  is  lost  by  doing  this.  If  it  is  still  de- 
sired to  compensate  for  the  reaction  due  to  the  propeller  toriiue,  more 
wash-out  is  given  on  one  side  than  on  the  other.  The  side  having  the  least 
wash-out  then  has  wash-in  relative  to  the  other  side. 


Fig.  41 — The  proper  way  to  lock  a  iurnhuckle 

Over-all  measurements. — Tighten  the  external  drift  wires  only  mod- 
erately tight.  The  following  over-all  measurements  should  now  be  taken, 
using  a  steel  tape  (see  Fig.  35)  :  Make  BA  =  DC  and  LH  =  MX.  Then 
OA  should  equal  OC  and  HE  should  equal  EX.  These  measurements 
should  be  made  at  points  on  the  upper  wing  panels  as  well  as  the  lower, 
making  eight  check  measurements  in  all. 


Fi<j.  42 — Individual  method  of  connect  in  (j  aileron  controls 


70  APPLIED  AERONAUTICS 

All  tiirnhucklcs  are  now  safetied  (Fig.  41).  Make  a  fjeneral  final 
inspection  of  the  mings  to  make  sure  that  nothing  has  been  overlooked. 
It  must  he  renicinhered  that  in  making  one  adjustment  other  adjustments 
made  preriouslg  mag  he  tJiroicn  sligJttlg  off,  so  that  when  the  wings  are 
finally  aligned  it  is  a  good  plan  to  check  the  lateral  dihedral,  stagger, 
angle  of  incidence,  etc.,  to  make  sure  that  all  are  correct. 

Controls-Ailerons. — Fasten  the  hand  wheel,  stick,  or  shoulder  yoke 
controlling  the  ailerons  in  its  central  position.  If  the  ailerons  have  brace 
wires  on  each  side  (see  Fig.  42 )  and  these  wires  are  supplied  with  turn- 
buckles,  straighten  up  the  trailing  edge  by  adjusting  these  wires.  If  the 
ailerons  are  connected  as  in  Fig.  43  the  trailing  edges  must  be  straight- 
ened as  the  ailerons  are  aligned  on  the  airplane. 

There  is  difference  of  opinion  about  drooping  the  trailing  edge  of 
ailerons  below  the  trailing  edge  of  the  plane  to  which  they  are  fastened. 
At  some  fields  the  turnbuckles  on  the  aileron  control  cables  are  so  ad- 
jiLSted  that  the  trailing  edge  of  the  aileron  lines  up  with  the  trailing  edge 


To/}  /^//eron  Wire 


Aileron  ConrtecZ/'n^   W/res 

^/^n/'no  Board 

^"^^  ioi/^er  Ai/eton 

Fig.  43 — Showing  series  method  of  connecting  ailerons  in  pairs 

of  the  wing  panel  to  which  it  is  hinged.  At  other  fields,  from  1/8  in.  to 
3/4  in.  of  droop  is  given  the  trailing  edge  of  the  aileron,  because  it  forms 
a  part  of  a  lifting  surface  and  it  is  reasoned  that  slack  will  be  taken  out 
of  the  lower  control  cables  when  the  machine  gets  into  the  air.  Unless 
directed  otherwise  it  perhaps  is  advisalde  to  give  little  or  no  droop. 

The  ailerons  should  work  freely  and  respond  quickly  with  no  feeling 
of  drag  when  the  hand  wheel  is  turned  or  the  stick  moved  even  very 


Profracfor  Leve/-^  Sfra/^hf  Edge 

Te<sf  fof  Sfroiphfness 

Fig.  44 — Trying  an  aligning  hoard  for  straightness 


ALIGNMENT 


71 


Test  of    Pf^oftvcfor  Lek'e/ 

Fig.  45 — Aligning  board  used  iritJi  table  for  lateral  dihedral  angles 

slightly.  Improper  coiling  of  cables  when  a  machine  is  dismantled  will 
ruin  this  condition  about  as  (juirkly  as  anytliing  could.  Care  must  be 
taken  not  to  put  too  much  tension  on  the  cables.  The  pulleys  around 
which  they  run  are  light,  and  not  always  so  strong  as  they  might  be. 
Cracked  pulleys  may  sometimes  be  found  on  old  machines. 

Interplane  ailerons  are  adjusted  so  that  both  are  in  the  same  plane 
when  control  is  neutral.  The  angle  at  which  they  are  set  must  be  given 
by  the  makers  or  determined  by  experiment  and  experience. 

Elerators. — Fasten  the  bridge  or  stick  control  in  its  central  position. 
Adjust  the  turnbuckles  on  the  control  cables  until  the  elevators  are  in 
their  neutral  position  and  both  are  in  the  same  plane.  Tighten  the  con- 
trol cables  enough  to  remove  lost  motion. 

Rudders. — Fasten  the  rudder  footbar  in  its  mid-position  and  adjust 
the  turnbuckles  until  the  rudder  is  in  the  neutral  position,  and  the  cables 
are  tight  enough  to  remove  lost  motion. 

Both  elevators  and  rudders  usually  carry  brace  wires  witli  turn- 
buckles which  can  be  used  in  straightening  their  trailing  edges. 

Notes  on  Aligning  Boards 

To  be  useful  an  aligning  board  first  of  all  must  be  true.  Fig.  44 
shows  a  method  of  testing  such  a  board  for  straightness.  ( See  A  and  B, 
Fig.  44.)  Also  by  supporting  the  board  as  shown  and  setting  the  pro- 
tractor level  at  different  degrees  the  protractor  can  be  tried  out.  Ref- 
erence to  the  table  for  lateral  dihedral  on  page  65  shows  the  differ- 
ence in  thickness  of  the  blocks  for  the  different  angles.  The  zero  point 
may  be  tested  by  setting  the  instrument  at  zero  and  supporting  the  align- 
ing board  on  some  surface  known  to  be  level. 

The  inclination  for  the  board  used  in  the  third  method  of  aligning 
for  lateral  dihedral  can  be  determined  from  the  lateral  dihedral  table. 
Fifty  inches  make  a  convenient  length  for  such  a  board  in  which  case 
the  Y  (see  Fig.  45)  is  just  half  of  that  given  in  the  table  for  lateral 
dihedral  ansles. 


Chapter  6 

CARE  AND  INSPECTION 

Cleanliness — Control  cables  and  wires — Locking  devices — Struts  and  sockets — Special 
inspection — Lubrication — Adjustments — Vetting  or  sighting  by  eye — Mishandling 
on  the  ground  —  Airplane  shed  or  hangar  • —  Estimating  time  —  Weekly  inspection 
card  form. 

CLEANLI]\TES8. — One  of  the  most  important  items  is  cleanliness  of 
all  parts  of  the  plane.  After  every  flight  the  machine  should  be 
thoroughly  cleaned.  To  remove  grease  and  oil  from  the  wings  and  covered 
surfaces,  use  either  gasoline,  acetone  or  castile  soap  and.  water.  If  castile 
soap  cannot  be  obtained,  be  sure  the  soap  used  contains  no  alkali  or  it 
will  injure  the  dope.  In  using  the  gasoline  or  acetone,  do  not  use  too 
much  or  it  will  also  take  off  the  dope.  A  good  way  to  use  the  latter  is 
to  soak  a  piece  of  waste  or  rng  and  rub  over  the  grease  or  oil,  then  wipe 
off  with  a  piece  of  dry  waste.  When  using  soap  and  water  be  careful 
not  to  get  any  inside  the  wing  as  it  is  liable  to  warp  the  ribs  or  rust  the 
wires. 

When  mud.  is  to  be  removed  from  the  surfaces  it  should  never  be 
taken  off  while  dry,  but  should,  be  moistened  with  water  and  then 
removed. 

Other  parts  of  the  nmchine  should  be  kept  thoroughly  clean  to  keep 
down  the  friction. 

Control  cables  and  wires. — All  cables  and  wires  should  be  inspected 
by  the  rigger  to  see  that  they  are  at  the  correct  tension.  Also  see  that 
there  are  no  kinks  or  broken  strands  in  any  of  the  cables  or  strands. 
Do  not  forget  the  aileron  balance  cable  on  top  of  the  wings.  When  a 
wire  is  found  to  be  slack  do  not  tighten  it  at  once  but  examine  the  op- 
posing wire  to  see  if  it  is  too  tight.  If  so  the  machine  is  probably  not 
resting  naturally.  If  the  opposing  wire  is  not  over-tight  then  tighten 
the  slack  wire. 

All  cables  and  strands  and  external  wires  should  be  cleaned  and 
re-oiled  about  every  two  weeks.  The  oil  should  be  very  thin  so  that  it 
will  penetrate  between  the  strands. 

LocJxing  devices. — All  threaded  fastenings  and  pins  should  be  in- 
spected very  frequently  to  see  that  there  is  no  danger  of  anything  com- 
ing loose. 

Struts  and  sockets. — Since  the  struts  are  compression  members, 
largely,  they  should  be  examined  on  the  ends  for  crushing  and  in  the 
middle  for  bending  and  cracking. 


CARE    AND    INSPECTION  71 

^^pccidl  ins[)crtioiL — A  detailed  inspecticm  of  all  parts  of  the  inaeliine 
should  be  made  ouce  every  Aveek.  Usually  there  is  an  inspection  sheet 
provided  for  this  purpose.  If  no  sheet  is  obtainable,  then  one  should  be 
made  before  the  inspection  is  started.  ^Make  a  list  of  all  the  parts  to  be 
inspected,  starting-  at  a  certain  point  on  the  machine,  and  following 
around  until  that  point  is  reached  again.  When  each  part  or  detail  is 
inspected  it  should  be  checked  on  the  sheet  as  defective  or  O.  K. 

A  good  weekly  inspection  card  form  is  given  on  pages  74  to  77. 

Luhrication. — Always  see  that  all  moving  parts  are  working  freely 
before  a  flight  is  made.  This  includes  undercarriage  wheels,  pulleys, 
control  levers,  hinges,  etc. 

Adjustments. — The  angle  of  incidence,  dihedral  angle,  stagger  and 
position  of  the  controlling  surfaces  should  be  checked  as  often  as  possi- 
ble so  that  everything  will  be  all  right  at  all  times.  Alignment  of  the 
undercarriage  should  be  made  so  that  it  will  not  be  twisted  and  thus  cut 
down  the  speed  of  the  machine. 

Yetting  or  sighting  hy  eye. — This  should  be  practiced  at  all  times. 
"NThen  the  machine  is  properly  lined  up,  look  at  it  and  get  a  picture  in 
your  mind  of  just  how  it  looks.  Then  when  anything  becomes  out  of  line 
it  can  be  easily  detected  without  using  any  tools.  See  that  the  struts  are 
in  the  same  plane  when  looking  at  the  front  or  side  of  the  machine.  The 
dihedral  angle  also  can  be  checked  by  this  method  of  sighting.  Some 
flyers  become  so  expert  that  they  can  check  the  alignment  of  the  whole 
machine  by  eye. 

Distortion 

Always  be  on  the  lookout  for  dislocation  of  any  of  the  parts.  If  any 
distortions  cannot  be  corrected  by  adjustment  of  the  wires,  then  the  part 
should  be  replaced. 

MishandUng  on  the  ground. — Great  care  should  always  be  taken  not 
to  overstress  any  part  of  the  machine.  Members  are  usually  designed 
for  a  certain  kind  of  stress  and  if  any  other  kind  is  put  upon  them,  some 
damage  is  likely  to  occur.  When  pulling  an  airplane  along  the  ground, 
the  rope  should  be  fastened  to  the  top  of  the  undercarriage  struts.  If 
this  cannot  be  done,  then  fasten  the  rope  to  the  interplane  struts  as 
low  down  as  possible. 

Never  lay  covered  parts  down  on  the  floor  but  stand  them  on  their 
entering  edges  with  some  padding  underneath.  Struts  should  be  stood 
on  end  where  they  cannot  fall  down. 

Hangar. — The  hangar  at  all  times  should  be  kept  in  the  best  possible 
condition.  Never  have  oily  waste  or  rags  lying  around  on  the  floor  or 
benches,  as  these  are  liable  to  catch  fire.  No  smoking  should  be  allowed 
in  or  near  the  building.  Do  not  have  oily  saw  dust  spread  around  on  the 
floor  to  catch  the  oil  but  have  pans  for  this  purpose. 

In  making  replacements  of  defective  parts,  have  a  place  for  the  old 
pieces.  Never  allow  them  to  be  put  where  they  will  be  mistaken  for 
new  parts. 


74  APPLIED  AERONAUTICS 

Each  tool  should  be  kept  in  a  certain  designated  place  and  when 
anybody  borrows  a  tool,  be  sure  that  he  puts  it  back  where  it  belongs. 

Estimating  time. — When  any  repairs  are  to  be  made,  learn  to  esti- 
mate the  time  required  for  the  job.  With  a  little  practice  this  can  be 
done  very  accurately.  It  may  help  some  time  in  making  a  report  to  an 
officer  in  charge  as  to  when  an  airplane  will  be  ready  to  go  out  again. 

Weekly  Airplane  Inspection  Card 

Date 191 

Airplane   No Make Model 

Engine  No Make Model 

Note :  This  card  must  be  made  out  by  Field  Inspector  for  every  machine 
under  his  charge,  signed  by  him,  and  must  be  turned  over  to  the  Chief  In- 
spector as  soon  as  made  out. 

I.,anding  gear: 

Wire   tension    

Wire   terminals    

Strut  sockets    (nuts,  bolts) 

Loose  spokes    

Axles  greased 

Security  of  wheels  to  axle 

Shock  absorber  rubbers 

Tire    inflation     

Propeller : 

Condition  of  blades 

Hub  assembly  (bolts,  washers,  cotters) 

Security   to    shaft 

Thrust    

Fuselage  nose : 

Tension  fuselage  bracing 

Tension  and  terminals  wing  drag  bracing 

Engine  bed  and  bolts 

Water  system: 

Leakage    

Radiator   full    

Engine : 

Valves — 

Intake  clearance    

Exhaust  clearance 

Spark  plugs — 

Clean    

Gap   

Carburetor — 

Security  to  manifold 

Bracing    

Manifold  joints    


CARE    AND    INSPECTION  75 

Oil  system : 

Leakage    

Oil  (grade)   

Oil   reservoir    full 

Magneto : 

Mounting    

Distributor  board 

Breaker  point  clearance 

Transmission    (drive)    wear 

Throttle  control: 

Pulleys 

Wiring   

Bell  cranks  and  connections 

Gasoline  system: 

Tank    

Gasoline  leads  and  connections 

Pump    

Gasoline  in  tank full 

Wing  joints : 

Lower  wing — right    

Lower  wing — left    

Upper  wing — right   

Upper  wing — left    

Wing  wires:  (tension,  terminals,  clevis  pins,  cotters,  safety  wires) 

Flying  wires — right  wing 

Flying  wires — left  wing    

Landing  wires — right  wing   

Landing  wires — left  wing 

Wires,  fittings,  turnbuckles,  cleaned  and  greased 

Wing  fittings :  (bolts,  nuts,  cotters) 

Right  wing,  upper lower 

Left  wing,  upper lower 

Struts : 

Sockets,  bolts,  cotters 

Straightness    

Right  wing   

Left  wing    

Ailerons : 

Straightness    

Hinge  assembly  (lubricate  with  graphite  grease). 

Security    

Wear    

Hinge  pins  and  cotters 

Control   wire,  connection    (mast) 

Frayed  control  wire  (wheel ) 

(pulleys  and  guides) 


76  APPLIED  AERONAUTICS 

Note :  Control  wires  frayed  at  any  part  of  their  length  must  be  re- 
placed at  once. 

Pulleys 

Greased    

Free  running 

Right  ailerons,   upper lower 

Left    ailerons,    upper lower 

Fuselage  rear  interior : 

Wire   tensions 

Longerons     

Fittings    

Alignment    

Stabilizer : 

Bolts,  nuts,  cotters,  braces 

Vertical  fin : 

Bolts,  nuts,  cotters,  braces 

Rudder : 

Hinge    assembly    

Security   

Wear    

Hinge  pins  and  cotters 

Control  wire  connections 

Mast    

Footbar    

Frayed    control    wire 

Note :     Control  wires  frayed  at  any  point  of  their  length  must  be  re- 
placed at  once. 
Pulleys 

Greased    

Free  running 

Elevators : 

Hinge  assembly 

Security    

Wear    

Hinge  pins  and  cotters 

Control   wire   connections — Mast 

Control  wire  connections — post 

Frayed  control  wire 

Note :  Control  wires  frayed  at  any  point  of  their  length  must  be  re- 
placed at  once. 

Pulleys    

Greased    

Free  running 

Right  elevator    

Left   elevator    


CARE  AND  INSPECTION  77 

Tail  skid : 

Skid    

Fittings    

Shock  absorber    

Controls : 

Free  and  proj^er  operation  (lubricate  with  graphite  grease) - 

Elevator  

Rudder  

Aileron    

Alignment  of  entire   machine: 


(Signed)  Field  Inspector. 


Chapter  7 

MINOR   REPAIRS 

Patching  holes  in  wings — Doping  patches — Terminal  loops  in  solid  wire — Terminal  splices 
in  strand  or  cable — Soldering  and  related  processes — Soft  soldering — Hard  solder- 
ing— Brazing — Sweating — General  procedure  in  soldering — Fluxes — Melting  points 
of  solders. 

THE  materials  used  in  patching  holes  in  linen-covered  surfaces  is 
unbleached  Irish  linen,  the  same  kind  as  used  in  covering  the  Avings. 
The  material  must  be  unbleached  or  it  will  not  shrink  the  required 
amount.  Generally  the  kind  of  dope  used  is  Emaillite  dope,  although 
the  acetate  or  nitrate  dopes  could  be  used.  The  dope  should  be  applied 
in  a  very  dry  atmosphere  or  on  a  sunshiny  day  at  a  temperature  not  less 
than  65  deg.  F.  A  brush  or  a  piece  of  svaste  may  be  used  to  apply  the  dope. 

In  patching  a  hole  the  first  thing  to  be  done  is  to  clean  the  surface 
of  the  old  dope.  To  do  this,  fine  sand  paper  may  be  used  or  acetone, 
gasoline  or  dope.  In  using  the  sand  paper,  care  should  be  taken  not  to 
injure  the  covering.  When  using  the  acetone  or  gasoline,  it  should  be 
put  on  the  surface,  allowed  to  stand  for  a  while  to  soak  up  the  old  dope, 
then  scraped  off.  The  same  method  is  applied  when  using  dope  to  clean 
the  surface. 

After  the  surface  is  cleaned,  the  edges  of  the  hole  should  be  sewed 
if  it  is  of  any  considerable  size.  To  do  this  sewing  linen  thread  and  a 
curved  needle  are  used.  The  stitches  should  not  be  closer  together  than 
1  in.  and  far  enough  back  from  the  edge  so  that  there  is  no  danger  of 
their  tearing  out.  With  a  small  hole,  such  as  a  bullet  hole  for  instance, 
it  is  not  necessary  to  do  any  sewing.  When  the  hole  is  several  inches 
square,  a  piece  of  unbleached  linen  should  be  sewed  in  to  give  a  body  for 
the  top  patch  so  that  it  will  not  be  hollow  in  the  center  after  it  is  dry. 
The  sewing  up  of  holes  should  be  done  after  the  surface  is  cleaned  so  that 
any  slackness  may  be  taken  up  before  the  patch  is  applied. 

After  sewing  is  finished  the  patch  is  cut.  It  should  be  made  about 
1  to  2  in.  larger  on  each  side  than  the  hole.  The  edges  of  the  patch  must 
be  frayed  for  about  ^  in.,  this  being  done  to  prevent  them  from  tearing 
easily. 

Dope  should  now  be  applied  to  the  wing.  Generally  several  coats 
are  put  on  so  that  there  will  be  a  sufficient  amount  to  make  the  patch 
stick  well.    After  the  last  coat  is  applied  the  patch  should  be  put  in  place 


MINOR  REPAIRS  79 

immediately  before  the  dope  has  a  chance  to  dry.  Any  air  bubbles  and 
wrinkles  should  now  be  worked  from  under  the  patch  by  rubbing  with 
the  fingers,  and  more  dope  put  on  top  of  the  patch.  Usually  there  are 
six  or  seven  coats  of  dope  applied  on  top  of  the  patch,  allowing  time  for 
each  coat  to  dry  before  another  is  applied. 

Any  small  amount  of  slackness  in  the  patch  will  probably  be  taken 
out  as  the  linen  shrinks.  If  the  patch  is  hollow  after  the  dope  is  thor- 
oughly dry,  however,  it  is  not  a  good  patch  and  should  be  removed.  A 
good  patch  should  be  tight  around  the  edges  as  well  as  in  the  center  over 
the  hole  and  should  contain  no  creases  or  air  bubbles. 

Terminal  Splices 

A  loop  or  splice  must  be  formed  in  the  end  of  every  brace  wire  or 
control  cable  where  it  is  attached  to  a  strut  socket,  turnbuckle,  control 
mast,  or  other  form  of  terminal  attachment.  The  manner  of  making 
the  loop  or  splice  in  the  wire  w  ill  vary  according  to  the  type  of  wire  or 
cable  used.  The  terminal  in  the  end  of  a  solid  wire  is  made  in  the  man- 
ner shown  in  Fig.  33. 

There  are  several  points  to  be  observed  in  making  this  type  of 
terminal  splice,  as  follows:  (a)  The  size  of  the  loop  should  be  as  small 
as  possible  within  reason,  as  a  large  loop  tends  to  elongate,  thus  spoiling 
the  adjustment  of  the  wires.  On  the  other  hand,  the  loop  should  not  be 
so  small  as  to  cause  danger  of  the  wire  breaking,  due  to  too  sharp  a  bend, 
(b)  The  inner  diameter  of  the  loop  should  be  about  three  times  the  diam- 
eter of  the  wire,  and  the  reverse  curve  at  the  shoulders  of  the  loop  should 
be  of  the  same  radius  as  the  loop  itself.  The  shape  of  the  loop  should  be 
symmetrical.  If  the  shoulders  are  made  to  the  proper  radius  there  will 
be  no  danger  of  the  ferrule  slipping  up  towards  the  loop,  (c)  When 
the  loop  is  finished  it  should  not  be  damaged  anywhere.  If  made  with 
pliers  there  will  be  a  likelihood  of  scratching  or  scoring  the  wire,  which 
would  weaken  it  greatly.  Any  break  or  score  in  the  surface  coating  of 
a  wire  destroys  the  protective  covering  at  that  particular  point  and 
the  wire  will  soon  be  weakened  by  exposure.  A  deep  nick  or  score  would 
greatly  weaken  the  wire  and  eventually  result  in  breakage  at  that  point. 

Splicing  a  strand  or  cable. — The  splice  in  the  end  of  a  strand  or 
cable  is  entirely  different  from  the  terminal  of  a  solid  wire.  The  end  of 
the  strand  is  led  around  a  thimble  and  the  free  end  spliced  into  the  body 
of  the  strand  or  cable  just  below  the  point  of  the  thimble.  Such  a  splice 
is  afterward  served  with  twine,  but  the  serving  should  not  be  done  until 
the  splice  has  been  inspected  by  whoever  is  in  charge  of  the  workshop. 
The  serving  might  cover  bad  workmanship  in  the  splice. 

Soldering. — Terminal  loops  or  splices  in  solid  wire  and  also  splices 
in  the  ends  of  strand  or  cord  are  sometimes  soldered  after  being  formed. 
There  are  some  objections  to  soldering  at  these  points,  however,  as  out- 
lined on  page  58.  The  ensuing  instructions  for  soldering  work  will 
prove  valuable  in  cases  where  this  method  of  securing  a  terminal  splice 
is  considered  desirable. 


80  APPLIED  AERONAUTICS 

Joininf/  of  metals  hi/  soldering  and  related  jyrocesses. — There  are  sev- 
eral methods  of  joining  metals  together  by  allovs  which  melt  at  a  lower 
temperature  thau  the  metals  to  be  joined.  These  processes  differ  in  tlie 
alloys  used  and  in  tlieir  melting  temperatures.  They  are  divided  into 
four  classes,  as  follows : 

(1)  Soft  soldering. — This  method  is  the  one  used  in  tin-smithing 
generally,  where  the  solder  is  melted  by  means  of  a  hot  soldering  copper 
over  the  surfaces  to  be  joined.  The  solder  used  in  this  process  has  a  low 
melting  point. 

(2)  Hard  soldering. — This  method  is  usually  used  in  jewelry  work 
and  in  the  arts,  where  a  higher  temperature  must  be  withstood.  The 
joining  metal  in  this  case  has  a  much  higher  melting  point  than  soft 
solder,  and  must  be  heated  with  a  blow-torch  to  make  it  flow. 

(3)  Brazing. — This  process  differs  from  hard  soldering  onh-  in  the 
fact  that  the  joining  metal  has  a  still  higher  melting  point.  It  is  used 
principally  in  motorcycle,  bicycle  and  automobile  construction,  where 
greater  strength  is  required. 

(4)  Sweating. — This  is  a  process  used  where  the  pieces  to  be  joined 
can  first  be  fitted  together,  then  individually  coated  with  solder,  then 
clamped  together  and  heated  until  the  solder  flows,  and  cements  them 
solidly  together.  This  method  allows  for  a  more  perfect  joint  being 
made.  The  more  accurately  the  parts  are  fitted  together  the  stronger 
the  union  will  be.  Also,  the  thinner  the  coat  of  soldering  material,  within 
reasonable  limits,  the  stronger  the  joint. 

All  of  the  above  methods  are  used  more  or  less  in  airplane  con- 
struction and  maintenance,  but  the  one  that  is  most  generally  used  is 
the  first,  or  soft-soldering  method. 

Cleanliness  is  of  prime  importance  in  making  joints  or  fastening 
by  any  of  these  methods.  In  soldering,  the  first  step  is  to  see  that  the 
soldering  copper  is  clean  and  well  tinned,  for  this  may  determine  the  suc- 
cess or  failure  of  the  job.  There  are  several  ways  of  cleaning  and  tinning 
the  soldering  copper,  but  the  one  recommended  is  to  heat  the  copper  to 
about  600  deg.  F.,  then  dip  the  point  quickly  into  a  cup  or  jar  containing 
ammonium  chloride  (NH4  CI)  and  granular  tin  or  small  pieces  of  solder. 
If  any  considerable  amount  of  work  is  to  be  done,  an  earthen  jar  or  a 
teacup  can  be  used,  and  kept  partly  filled  with  this  mixture. 

Tinning  Soldering  Coppers 

Another  way  of  tinning  the  soldering  copper  is  to  make  a  depression 
in  a  piece  of  sheet  tin  and  place  in  it  a  small  quantity  of  soldering  flux 
together  with  a  piece  of  solder.  File  the  copper  until  bright,  heat  it  to 
about  600  deg.  F.,  and  then  move  it  around,  while  hot,  in  the  depression 
in  the  tin  until  it  becomes  coated  with  molten  solder.  It  will  now  be 
ready  to  use. 

The  next  step  is  to  clean  thoroughly  the  parts  to  be  joined,  using 
fine  emery  cloth,  sandpaper  or  a  scraper.  If  the  parts  are  of  raw  ma- 
terial, sandpaper  will  do,  but  if  they  are  old  parts  which  previously  have 


MINOR  REPAIRS  81 

been  exposed,  or  if  a  heavy  oxide  has  formed,  the  surfaces  to  be  soldered 
should  be  filed  or  scraped  until  perfectly  bright  and  clean.  The  cleaned 
surface  should  then  be  covered  with  soldering  fluid  or  one  of  the  luanj- 
soldering  pastes. 

Heat  the  soldering  copper  to  about  600  dog.  F.,  and  touch  it  to  the 
solder,  being  careful  to  get  only  a  small  amount  of  solder  on  the  copper. 
Rub  the  copper  over  the  surfaces  to  be  joined  until  a  bright,  even  coating 
of  solder  clings  to  the  surfaces.  Place  the  pieces  together  and  heat  until 
the  solder  flows,  using  the  hot  copper  to  furnish  the  necessary  heat  and 
adding  more  solder  as  needed.  Care  must  be  taken  not  to  overheat  the 
pieces  at  the  joint,  as  this  has  a  tendency  to  weaken  the  metal  at  that 
point  and  may  cause  trouble. 

The  same  general  procedure  as  the  above  is  followed  for  hard  solder- 
ing, -uith  the  exception  that  a  higher  temperature  must  be  applied. 

Fluxes 

Fluxes  are  used  in  soldering  to  prevent,  so  far  as  possible,  the  forma- 
tion of  oxides  on  the  heated  surfaces,  and  to  flux  off  those  that  may  have 
formed.  Acid  fluxes  are  the  most  effective  and  on  iron  or  steel  are  prac- 
tically necessary.  The  objection  to  their  use  is  that  unless  the  parts  are 
thoroughly  cleaned  after  soldering  the  acid  in  the  flux  attacks  and  cor- 
rodes them. 

In  the  case  of  stranded  wires  or  cables  the  flux  will  penetrate  into 
the  minute  spaces  betw^een  the  strands  and  will  be  extremely  difficult  to 
remove  or  neutralize,  even  when  the  cable  or  wire  is  washed  with  or 
dipped  in  an  alkaline  solution,  such  as  soap  or  soda  water. 

Some  of  the  fluxes  in  general  use  are : 
Zinc  chloride  (Zn  CI),  corrosive. 
Dilute  muriatic  acid  ( H  CI ) ,  corrosive. 

Resin,  non-corrosive.     This  is  satisfactory  for  tin.  but  will  not 
work  on  galvanizing. 

Resin  and  sperm  candle  melted  together  make  a  fair  non-corrosive 
paste.  For  either  tin  or  galvanizing  use  three  parts  resin  to  one  part 
sperm  candle.  Sometimes  better  results  are  obtained  on  dirty  surfaces 
by  adding  one  part  alcohol  to  this  mixture. 

Melting  points  of  solders. — The  melting  points  of  solders  composed 
of  tin  and  lead  in  various  proportions  are  as  follows : 


Proportion 

Melting 

Tin 

Lead 

Point 

1     part 

25  parts 

558  deg.  F. 

1     part 

5  parts 

511  deg.  F. 

1     part 

1  part 

370  deg.  F. 

11  parts 

1  part 

340  deg.  F. 

5     parts 

1  part 

278  deg.  F. 

A  composition  of  1  to  1  is  most  commonly  used  for  tin-smithing. 
For  electrical  work  where  the  solder  is  used  in  the  form  of  wire,  a  pro- 
portion of  li  to  1  or  2  to  1  is  used. 


Chapter  8 

INSTRUMENTS 

Compass — Magnetic  errors — Variation — Deviation — Corrections — Napier  diagram — Heel- 
ing errors — Magnetic  clouds — Aneroid  barometer — Errors — Uses — Altimeter — Er- 
rors— Banking  meter — Air  speed  indicator — Incidence  indicator — Sperry  Clinom- 
eter— Automatic  drift  set — Bourdon  gauge — Radiator  thermometer. 

T  TXDOUBTEDLY  the  compass  is  one  of  the  most  important  instru- 
^^  ments  on  an  airplane  and  a  tliorongh  knoAvledj»e  of  its  construc- 
tion, operation  and  theory  are  absolutely  essential  to  enable  the  student 
to  become  a  successful  pilot. 

Theoretically,  a  compass  is  a  permanently  magnetized  needle  swing- 
ing freely  in  a  horizontal  plane  on  a  pivoted  point  and  indicating  a  north 
and  south  direction,  due  to  the  attraction  of  the  earth's  magnetic  north 
pole  for  the  north  pole  of  the  compass  needle,  and  the  repulsion  of  the 
magnetic  pole  for  the  south  pole  of  the  compass  needle.  As  is  the  case 
with  all  mechanisms,  this  theory  has  been  cimibined  with  modern  refine- 
ments, until  we  find  in  jjractice  at  the  present  time  two  main  types  of 
compass,  viz.,  the  dry  card  compass  and  the  liquid  compass. 

The  dry  card  compass  consists  of  a  graduated  card  over  which  the 
magnetized  needle  swings  freely.  The  accompanying  cut  (Fig.  47)  il- 
lustrates such  a  graduated  card,  which,  in  a  much  smaller  form,  is  in  use 
as  a  pocket  compass.  It  can  readily  be  seen  that  such  an  instrument  is 
very  easily  disturbed,  the  slightest  jar  starting  it  dancing.  Gun  fire 
would,  of  course,  render  it  useless.  Another  very  prominent  defect  is  its 
inability  to  come  to  a  complete  rest  without  considerable  oscillation.  To 
overcome  these  mechanical  errors  the  U.  S.  Xavy  produced  the  liquid 
compass  now  used  on  all  vessels,  and.  in  a  more  perfected  form,  on  air- 
planes. 

The  construction  is  somewhat  more  complex  as  illustrated  by  Fig.  46, 
which  is  a  cross-section  of  a  Creagh  Osborne  standard  airplane  compass. 
Instead  of  a  needle  swinging  over  a  graduated  card,  this  compass  has  a 
graduated  card  swinging  past  a  certain  point  or  line  marked  on  the  in- 
side of  the  compass  case,  called  the  "lubber  line,"  the  entire  mechanism 
being  immersed  in  an  airtight  bowl  of  liquid. 

In  detail  the  construction  is  as  follows :  M  is  a  pivot  supporting  the 
graduated  dial  P,  the  latter  being  made  of  tinned  brass  -and  graduated 
in  quarter  points  and  half  degrees.  This  dial  is  hollow  and  airtight, 
having  in  the  center  a  spheroidal  air  chamber  Q  to  buoy  up  the  weight 


INSTRUMENTS 


83 


of  the  card  and  iiiauiicts  ( ).  allowinu  a  pressure  of  between  60  and  90 
grains  on  the  pivot  at  r>0  de*i.  F.  The  ])iv()t  rests  in  a  socket  whose  bot- 
tom X  is  a  sappliire  jewel  to  form  a  bearin<i.  At  the  base  of  tlie  column 
is  a  telescopic  sprinn'  T  to  ease  the  jars  on  this  jewel.  The  magnets  O 
consist  of  four  highly  magnetized  bundles  of  steel  wires  contained  in  a 
sealed  cylindrical  case,  the  magnets  i)laced  parallel  to  the  north  and 
south  line  of  the  card,  and  so  aligned  that  their  entire  directive  force 
will  cause  the  north  point  of  the  card  to  point  to  magnetic  north.  The 
card  is  mounted  in  a  cast  bronze  bowl  I)  which  is  entirely  filled  with 
liquid — 45  percent  alcohol  and  55  percent  distilled  water.  Beneath  the 
bowl  is  a  self-adjusting  expansion  chamber  K  of  elastic  metal,  arranged 
with  a  small  hole  L.  to  permit  circulation  of  the  liquid  between  the  bowl 
and  expansion  chamber.  The  expansi<m  chamber  is  so  designed  as  to 
expand  Avith  a  rise  in  temperature  and  counteract  the  expansion  of  the 
liquid  in  the  bowl,  thus  keeping  the  bowl  free  from  bubbles.  At  one  side 
is  a  filling  screw  through  which  the  air  bubbles,  which  are  bound  to 
appear,  may  be  removed,  and  additional  liquid  added. 


Fi<j.  46 — Details  of  the  CreayJi  Osborne  air  plane  compass 


84 


APPLIED   AERONAUTICS 


The  graduations  on  the  card  are  marked  every  20  degrees,  the  0  being 
dropped  to  avoid  crowding.  These  markings  are  insoluble  in  the  liquid 
and  are  visible  at  night.  The  compass  bowl  sets  in  an  outer  bowl  B  of 
the  same  material.  It  rests  on  rubber  supports,  and  between  the  two 
bowls  is  a  packing  of  horsehair  for  absorbing  shock.  Beneath  the  com- 
pass are  the  corrections  for  various  magnetic  effects  which  will  be  dis- 
cussed later. 

It  will  be  recalled  that  the  dry  card  compass  was  subject  to  oscilla- 
tion and  was  easily  disturbed.  It  is  obvious  that  in  the  liquid  compass 
both  these  errors  are  materially  reduced,  the  liquid  tending  to  dampen 


Fig.  47 — Standard  compass  card 


the  oscillatory  motion,  or  magnetic  moment,  as  it  is  called,  and  also  pre- 
venting the  needle  from  dancing  about  the  x)ivot  point.  In  addition,  the 
combined  effect  of  the  small  but  powerfully  magnetized  wires  is  to  give 
the  system  a  greater  sensibility  or  directive  force. 

Magnetic  Errors 

Variation. — The  errors  previously  discussed  have  been  mechanical 
in  nature  and  within  the  compass  itself.  There  is  another  class  of  errors, 
affecting  compasses  of  all  types,  which  are  clue  to  external  influences, 
and  a  thorough  knowledge  of  their  various  actions  is  absolutely  essential 
to  the  use  of  the  instrument. 

These  may  be  called  ''magnetic"  errors,  inasmuch  as  they  are  due 
either  directlv  or  indirectlv  to  the  magnetic  influence  of  the  earth  itself. 


INSTRUMENTS  85 

Consider  the  earth  as  a  huge  magnet  having  a  north  and  soutli  magnetic 
pole.  The  north  magnetic  pole  and  the  north  geogi-aphical  pole  do  not 
coincide  in  location.  Tlie  true  north  or  geographic  north  is  Avhat  we  call 
the  north  pole  and  is  the  northernmost  point  on  the  earth's  surface.  The 
magnetic  north  pole  is  located  near  the  northern  part  of  the  Hudson  Baj 
region,  and  is  so  called  because  the  earth's  magnetic  influences  in  the 
northern  hemisphere  reach  a  maximum  at  this  point.  Inasmuch  as  the 
north-seeking  end  of  the  compass  needle  points  to  this  point,  it  can  readily 
be  seen  that  there  is  an  error  between  the  true  nortli  and  the  compass 
reading.  This  error  is  called  the  variation  and  is  known  and  tabulated 
for  all  points  on  the  earth's  surface.  It  changes  slightly  from  year  to 
year,  but  for  air  work  we  can  consider  it  as  constant  for  any  point,  and, 
as  the  compass  cannot  be  mechanically  corrected  for  it,  the  variation 
must  always  be  included  in  the  calculation  of  bearings. 

Depends  on  Locality 

Variation  may  be  either  easterly  or  westerly,  depending  on  the  loca- 
tion on  the  earth's  surface;  if  easterly,  it  is  given  a  positive  sign,  if  west- 
erly it  is  considered  negative  in  sign.  These  signs  or  directions  are  de- 
termined by  the  observer  who  is  considered  as  being  at  the  center  of  the 
compass  and  facing  the  point  under  consideration.  It  must  of  course 
be  understood  that  all  conditions  are  reversed  in  the  southern  hemi- 
sphere. In  this  connection  it  might  be  interesting  to  note  that  the  vari- 
ation in  Flanders  amounts  to  about  14  deg.  and  is  westerly.  Hence  to  fly 
true  north  from  any  point  in  that  region  the  compass  will  read  14  deg. 
[3G0  deg.  -  (-11  deg.)].  The  compass  being  graduated  from  zero  to 
3G0  deg.,  the  following  rule  may  be  formulated  for  finding  the  compass 
course  from  the  true  course:  "Always  subtract  the  variation  (neglecting 
sign)  if  easterly,  and  add  it,  if  westerly,  from  the  true  course,  in  order 
to  get  the  compass  course." 

Deviation. — Again  let  us  consider  the  earth  as  a  huge  magnet  with 
lines  of  force  flowing  between  the  poles  like  invisible  rubber  bands.  If 
an  iron  rod  is  held  parallel  to  these  lines  of  force,  i.  e.,  approximately 
north  and  south,  and  then  struck  two  or  three  sharp  blows,  it  will  be 
found  by  bringing  it  to  a  compass  needle,  that  one  end  either  attracts  or 
repels  the  needle,  thereby  indicating  that  the  rod  has  become  magnetized. 
Xow,  if  the  rod  be  reversed,  end  for  end,  and  the  experiment  repeated, 
it  will  be  found  that  the  magnetism  has  become  reversed.  In  other  words, 
there  has  been  induced  into  an  iron  rod,  a  certain  amount  of  magnetism, 
which  is  called  "induced  magnetism."  If  the  rod  is  of  hard  iron  it  will 
remain  a  permanent  magnet,  but  if  it  is  of  soft  iron  it  will  lose  the  mag- 
netism as  soon  as  the  inducing  influence  is  removed.  It  readily  can  be 
seen  from  the  above  exjjeriment  that  in  the  construction  of  an  airplane 
there  is  a  certain  amount  of  magnetism  induced  into  the  iron  and  steel 
parts  of  the  engine,  beams,  wires,  etc.,  due  to  hammering.  Such  a  mag- 
netism is  knoAvn  as  "residual"  or  "sub-permanent"  magnetism,  and  the 
error  which  it  produces  in  the  compass  is  called  "deviation." 


86 


APPLIED   AERONAUTICS 


Correction  for  suh-periiifiiieiif  iiKifincflHui. — There  are  two  methods 
of  correction  for  sub-permanent  maj^uetism,  both  of  which  are  rather 
teclinical  in  theory,  but  sinij)le  in  practice.  The  first  is  by  means  of  small 
"adjustino-  magnets,"  and  the  second  is  ''Napier's  diagram."  No  at- 
tempt will  be  made  to  explain  the  theory  of  either  method,  but  simply 
liow  they  operate  in  actual  practice.     It  should  be  added  that  Napier's 


Fig.  48 — Model  sJiOic'ni;/  Jiow  corrections  are  made  for  residual  or  sub- 

pernianeiit  uia</netisiii 

diagram  is  a  simple  method  of  finding  a  talde  of  corrections  rather  than 
elimination  of  the  deyiation. 

Fig.  48  is  a  model  \yhicli  seryes  to  illustrate  the  method  of  correc- 
tion for  sub-permanent  magnetism  by  means  of  small  adjusting  mag- 
nets. AiV  represents  a  ship  which  can  be  rotated  in  a  horizontal  plane 
aboye  the  axis  B  and  so  placed  that  the  center  line  of  the  ship  has  the 
true  magnetic  bearing  indicated  by  the  dial  D.  The  compass  is  fastened 
to  the  block  which  rotates  with  the  ship  AA.     The  sub-permanent  mag- 


INSTRUMENTS 


87 


iietism  is  roin-escnted  by  tlio  iiiaunots  MM  which  can  l»t^  i)laocd  in  any 
position.  Practice  lias  sliown,  however,  that  one  magnet  is  better  than 
two.  These  magnets  are  used  merely  to  illustrate  the  method.  In 
actual  jn-actice  tlie  metal  i)arts  of  the  shij)  or  airplane  take  their  place. 
Small  correcting  magnets  s  and  t  are  held  by  the  standard  S  over 
the  vertical  axis  of  the  compass.    Their  distance  can  be  varied  by  means 


Fig.  49 — Mariner's  coiiipass 


of  the  small  holes  as  shown.  These  small  magnets  may  be  placed  either 
above  or  below  the  compass  as  long  as  they  are  in  the  plane  of  its  vertical 
axis.  The  compass  is  then  corrected  by  raising  or  lowering  these  mag- 
nets. The  following  directions  explain  in  detail  how  an  airplane  com- 
pass is  corrected : 


88  APPLIED   AERONAUTICS 

1.  Place  the  airplane  in  the  true  magnetic  north  and  south  flying 
position  (almost  every  airdrome  has  some  cement  cross  or  stakes  to 
mark  these  positions). 

2.  Bring  down  one  of  the  small  adjusting  magnets  over  the  compass 
in  an  east  or  west  position.  If  deviation  increases  reverse  the  magnet 
end  for  end  and  again  lower  it  over  the  compass  until  the  deviation  is  zero. 

3.  Fix  the  magnet  at  that  height  above  the  compass  at  which  devi- 
ation is  zero. 

4.  Turn  the  plane  to  a  true  magnetic  east  and  west  flying  position. 

5.  Repeat  2  and  3,  using  another  adjusting  magnet  and  being  sure 
to  apply  it  in  an  east  and  west  position. 

6.  Check  on  other  magnetic  bearings. 

In  summarizing  this  method  there  are  a  few  salient  facts  to  be  em- 
phasized. The  adjusting  magnets  must  always  be  applied  in  an  east 
and  west  position  regardless  of  the  heading  of  the  ship  or  plane.  After 
the  position  of  a  correcting  magnet  has  been  determined  it  can  be  turned 
in  any  direction  simultaneously  with  the  compass  without  destroying  its 
effect.  In  actual  practice  the  corrections  are  usually  placed  below  the 
compass  in  receptacles  arranged  for  that  purpose.  This  is  shown  in 
Pig.  49,  which  is  an  illustration  of  a  mariner's  compass,  or  by  referring 
back  to  Fig.  46,  F.  The  correction  is  not  a  permanent  one,  and  from 
time  to  time  should  be  checked. 

^  Napier  Diagram 

Najner  diagram. — The  second  method  of  correcting  for  sub-perma- 
nent magnetism  is  by  means  of  Napier's  diagram,  an  illustration  of  which 
is  shown  on  page  87.  The  diagram  is  nothing  more  or  less  than  a  gTad- 
uated  compass  card  straightened  out  into  a  straight  line.  This  method 
does  away  with  the  small  iron  correctors.  Referring  back  to  Fig.  48, 
assume  an  airplane  AA  rotating  in  a  horizontal  plane.  The  magnets 
MM  represent  the  sub-permanent  magnetism  causing  deviation  of  the 
compass;  in  practice  the  metal  parts  of  the  engine  and  plane  have 
the  same  effect. 

To  plot  deviations  on  the  Napier  diagram. — Obtain  the  compass 
reading  for  the  true  magnetic  course  at  each  of  the  cardinal  points  of 
the  compass.  If  the  reading  is  greater  than  the  true  course  the  devi- 
ation should  be  plotted  on  the  left  side  of  the  chart.  If  the  reading  is 
less  than  the  true  course,  plot  the  deviation  on  the  right  side  of  the  chart. 
Mark  on  the  center  scale  of  the  diagram  the  compass  reading  for  a  given 
true  magnetic  course,  north  or  0  for  instance,  then  draw  a  line,  paral- 
leling the  dotted  lines,  from  the  compass  reading  to  the  solid  line  from 
the  corresponding  true  magnetic  course.  Follow  the  same  procedure 
for  each  of  the  cardinal  points  of  the  compass  for  which  readings  were 
taken,  then  draw  a  curve  through  the  points  at  which  the  dotted  lines 
projected  from  the  compass  readings  intersect  the  solid  lines  from  the 
corresponding  true  magnetic  courses.  From  this  ciTrve  the  deviation 
for  any  course  can  be  plotted. 


INSTRUMENTS 


89 


To  ohtaiii  course  to  he  steered  for  a  given 
trite  magnetic  course. — From  the  point  ou 
the  center  scale  representing  the  true  mag- 
netic course  desired  project  a  line  parallel 
to  the  solid  lines  until  it  intersects  tlie 
curve  already  plotted.  From  this  point 
project  another  line  parallel  to  the  dotted 
lines  back  to  the  center  scale.  The  point 
at  which  this  last  line  intersects  the  center 
scale  gives  tlie  course  to  be  steered. 

A  homely,  but  easily  remembered  rule 
for  the  use  of  a  Napier  diagram  is  given 
below : 


Sh/p's 

H&acf 

Compass- 
Degrees 

Dei^/a//on- 

Magnetic 

De^re^S 

N 

0 

28     -^ 

^'28 

N.E. 

45 

80    ^ 

-35-^^ 

£. 

90 

1/8    '-^^ 

'28   ^ 

S.£ 

/35 

/45    -- 

^^-/O 

S 

/do 

/7/     — 

-^^i^ 

3.h< 

225 

/99    — 

—*26 

IV. 

270 

236   -~~~~ 

_jfj<? 

MH< 

3/5 

289  -\ 

*2e 

N. 

360 

388  ^ 

^^-28 

\ 


"If  you  wish  to  steer  the  course  allotted. 
Depart  by  plain,  return  by  dotted; 
From  compass  course,  magnetic  to  gain, 
Depart  by  dotted,  return  by  plain." 


Fig.  50 — Najner  diagrarii  shoming  method  of 
plotting  deviation  curve 


90 


APPLIED   AERONAUTICS 


A  Napier  diagram  is  shown  in  Fig.  50  togetlier  with  a  sample  table 
jjiving  assumed  compass  readings  for  the  cardinal  compass  points,  and 
showing  how  the  curve  is  plotted  from  these  compass  readings. 

HeeJinq  error. — In  all  previous  discussions  the  force  of  sub-perma- 
nent magnetism  has  been  considered  as  acting  only  in  a  horizontal  plane. 
It  can  readily  be  seen  from  the  accompanying  sketch  that,  when  the  ves- 
sel heels  to  port  or  starboard  the  horizontal  and  vertical  components 


it 


y 


Ship  heoding     North. 


» 


® 


Hee/ed  to  Pori:     U^nc^ht    Heeled  fo  Storboard. 


On  even 


Heeled 


Heeled 


® 


Heel. 


to  Port 


to   Storboord. 


Ship   heoding  East. 
Fig.   51 — ^lioicing  compass  error  due  to   heeVuig  of  ship    when    headed 


north  or  south 


INSTRUMENTS 


91 


change  jjosition  to  a  cei-tain  extent,  piodiicinii-  a  resultant  force  which 
acts  on  the  needle.  This  is  the  "heeling;"  error  and  as  the  illustration 
shows,  it  is  a  maximum  when  the  ship  is  heading  north  or  south  and  zero 
when  east  or  west.  Being  due  to  vertical  forces  it  is  corrected  by  a  single 
vertical  magnet  placed  directly  in  the  vertical  axis  of  an<l  at  a  certain 
distance  below  the  compass  while  the  airplane  is  ui)right.  This  is  illus- 
trated by  H  in  Fig.  46.  Tn  the  northern  hemisphere  the  noith  })olc  of 
this  magnet  will  be  up. 

Magnetic  clouds. — A  third  form  of  error,  more  or  less  mechanical, 
should  also  be  mentioned.  It  is  based  on  the  erroneous  supposition  that 
the  clouds  exert  a  nuignetic  influence  on  the  compass  needle,  due  to  the 
fact  that  on  entering  a  cloud,  the  card  may  be  observed  to  turn  of  its 
own  accord.  The  theory  that  clouds  exert  a  magnetic  influence  has  been 
put  forth  in  explanation.  Ordinary  clouds  are  not  magnetic  —  only 
thunder  clouds — and  the  aviator  does  not  usuallv  flv  in  thunderstorms. 


Fig.  52 — Standard  form  of  airplane  compass 


The  magnetism  of  the  earth  causes  the  north  end  of  the  needle  or 
card  to  dip  in  the  northern  hemisphere,  the  angle  varying  from  0  deg.  at 
the  equator  to  90  deg.  at  the  magnetic  north  pole.  To  offset  this,  the 
south  pole  of  the  compass  is  weighted  slightly.  If  a  machine  be  flying 
north,  and  turns  to  right  or  left,  centrifugal  force  acts  on  the  needle, 
causing  the  southern  end  to  swing  out  an<l  the  northern  end  to  swing  in, 
\\hen  exactly  the  reverse  should  take  ])lace.  If  a  pilot  is  unaware  of  this 
action,  he  is  verv  liable  to  increase  his  turn  still  more,  thercbv  increasing 


92 


APPLIED   AERONAUTICS 


liis  error.  lu  time  tlie  inomeutnni  may  cause  the  card  to  swing  com- 
pletely around,  as  is  often  the  case.  If  the  aviator  has  any  point  to  steer 
by  he  can  hold  the  machine  steady  until  the  card  has  settled  down.  The 
only  way  to  correct  this  error  is  to  make  the  needle  a  Tery  weak  magnet, 
thus  requiring  a  very  small  weight  on  the  south  end  to  offset  the  dip. 

The  aviator  should  examine  his  compass  with  a  view  to  finding  out 
if  it  is  subject  to  this  error.  Compasses  with  a  short  period  of  vibration 
are  likely  to  be  wrong ;  those  with  a  long  period  are  usually  right. 

Summary. — This  completes  the  discussion  of  the  main  errors  of  the 
compass.  There  remain  a  few  forms  of  error  which  are  to  be  studied 
only  in  the  case  of  the  mariner's  compass,  and  which  are  too  delicate  to 
be  considered  in  aerial  work.  The  student  should  acquire  the  habit  of 
constantly  checking  the  instrument  when  in  flight  by  bearings  or  rivers, 
roads,  bridges,  towns,  etc.,  over  which  he  passes.  This  cannot  be  too 
strongly  emphasized. 

Figs.  52  and  53  are  illustrations  of  two  forms  of  compass  now 
in  use  on  airplanes,  the  latter  being  a  Creagli  Osborne  type,  a  cross 
section  of  which  is  shown  in  Fig.  46. 

The  Aneroid  Barometer 

Fundamental  principles  of  air  pressure. — If  a  glass  tube  sealed  at  one 
end  and  completely  filled  with  mercury  is  inverted  into  a  boAvl  of  the  same 
liquid  and  allowed  to  run  out,  it  will  be  found  that  the  mercury  in  the 


r 

~\ 

/^ 

^^Kfk 

*^€^^ 

Aw 

^ ' ,.  j^Pl 

B'^'^'IIh 

a  m 

/  ^^Pi^ 

s      M^l 

Iv 

'^H^^- 

^#H 

^ 

W\ 

mt.. 

\ 

Fig.  53 — Creagli  Osborne  type  of  airplane  compass 


INSTRUMENTS 


93 


Fig.  54 — Ane7^oid  barometer  with  cover  reinoced 

tube  drops  a  total  of  approximately  30  in.  This  experiment  indicates 
that  the  air  has  Axeight,  this  weight  exerting  a  pressure  sufficient  to 
maintain  the  column  of  mercury  in  the  tube  up  to  about  30  in.  from  the 
top.  Calculation  shows  that  the  pressure  amounts  to  about  14.7  lbs. 
per  square  inch  at  sea  level.  This  experiment  also  illustrates  in  a  simple 
way  the  theory  and  construction  of  the  mercurial  barometer,  Avhicli  is 
used  in  all  measurements  of  atmospheric  pressure.  At  the  same  time  it 
readily  can  be  seen  that  such  an  instrument  would  be  entirely  imprac- 
ticable for  use  on  an  airplane.  Hence  for  use  in  aerial  work  there  is 
used  what  is  known  as  the  aneroid  barometer,  an  illustration  of  whicL 
is  shown  in  Fig.  54. 

Construction  of  aneroid  barometer. — The  aneroid  barometer  receives 
its  name  from  the  word  "aneroid"  which  means  "without  fluid."  Its  con- 
struction is  very  simple,  and  in  detail  is  as  follows :  In  place  of  the  col- 
umn of  mercury  there  is  a  German  silver  corrugated  expansion  chamber 
M  (see  Fig.  54)  connected  by  a  post  P  to  a  steel  leaf  spring  S  which  in 
turn  is  connected  to  a  pivot  A.  The  spring  is  also  connected  b}'  a  lever 
arm  L  and  a  system  of  levers  IJ  to  a  post  supported  by  a  table  T.  This  has 
a  chain  gear  mechanism  at  C  operating  the  indicator  G.  A  hair  spring  H 
is  fitted  which  serves  to  take  up  any  slight  shock  due  to  loose  connections. 
Any  elevation  or  depression  of  the  expansion  chamber  due  to  change  in 
barometric  pressure  raises  or  lowers  the  leaf  spring,  which  in  turn  com- 
uiunicates  this  action  by  means  of  the  lever  arm  and  system  of  levers  to 
tlie  indicator.  The  leaf  spring  also  serves  the  purpose  of  maintaining  a 
constant  tension  upon  the  expansion  chamber  and  the  indicator. 

Errors. — The  aneroid  is  not  an  absolutely  accurate  measurement  of 
air  pressure.     It  does  not  permit  of  the  numerous  refinements  of  mech- 


94  APPLIED   AERONAUTICS 

aiiisni  necessary  to  coiupeiisate  for  the  various  conditions  that  must  be 
taken  into  consideration  in  atmospheric  measurements.  It  is  absolutely 
necessary  that  the  entire  system  be  rigidly  connected,  otherwise  any 
small  change  in  the  expansion  chamber  Avould  mereh'  serve  to  overcome 
the  slack  in  the  mechanism.  In  otlier  words  there  must  be  a  perfect 
balance  of  the  system.  For  this  reason  sudden  changes  in  temperature 
affect  it  verj  seriously,  bringing  about  looseness  in  the  joints,  and  in- 
creases in  friction.  As  it  is  not  designed  to  compensate  for  these  changes, 
the  readings  may  often  be  in  error.  By  tapping  the  aneroid  at  different 
points,  errors  due  to  slack  or  lack  of  balance,  may  be  detected. 

Uses  of  the  aneroid  haroiiieter. — The  most  common  use  of  the  aneroid 
in  aviation  is  for  determining  changes  in  elevation,  in  which  use  it  gen- 
erally appears  as  a  pocket  aneroid.  It  is  very  frequently  used  in  con- 
nection with  sounding  balloons  for  determining  atmospheric  conditions 
at  higher  levels,  Such  aneroids  are  self-recording  and  are  known  as 
barographs. 

The  Altimeter 

The  theorj^,  construction,  and  operation  of  the  altimeter  are  practi- 
cally the  same  as  the  aneroid  barometer.  It  is  primarily  an  instrument 
for  measurement  of  altitude  and  is  very  often  combined  with  the  aneroid 
in  which  case  it  is  known  as  the  aneroid  altimeter.  There  are,  however, 
certain  conditions  that  must  be  considered  in  the  graduations  of  the 
altimeter  that  are  not  considered  with  the  aneroid.  It  was  shown  that 
the  atmosphere  exerts  a  pressure  of  approximately  14.7  lbs.  per  square 
inch  at  sea  level.  Observation  has  proven  that  this  pressure  does  not 
vary  directly  with  the  altitude.  In  fact,  half  the  earth's  atmosphere  is 
included  in  the  first  three  and  one-half  miles  above  the  earth's  surface, 
and  it  is  assumed  that  traces  of  our  atmosphere  can  be  found  even  as  high 
as  two  hundred  miles.  From  this  it  readily  can  be  seen  that  at  an  alti- 
tude of  two  miles  the  pressure  will  not  be  one-half  as  much  as  at  one 
mile.  The  pocket  aneroid  altimeter  is  accordingly  graduated  to  meet 
these  conditions,  smaller  graduations  occurring  at  the  higher  altitudes. 

The  altimeter  in  general  use  in  aerial  work  is  graduated  as  in  Fig. 
55,  Note  that  the  graduations  are  equal.  This  is  compensated  for  by  a 
somewhat  complicated  system  of  levers  within  the  instrument  itself.  The 
altimeter  is  so  constructed  that  it  may  be  adjusted  for  any  elevation 
above  sea-level  at  which  the  pilot  may  be,  this  being  done  by  rotating 
the  dial  until  the  zero  and  needle  are  coincident.  This  adjustment  is 
provided  to  enable  the  pilot  to  tell  at  a  glance  his  actual  altitude  above 
the  ground,  without  having  to  make  allowances  for  the  height  of  the 
ground  above  sea-level.  This  latter  might  be  a  very  few  feet  or  several 
thousand,  depending  on  the  locality. 

Errors  of  the  altimeter. — The  altimeter  is  subject  to  the  same  eiTors 
as  the  aneroid  but  it  is  highly  important  that  these  errors  be  taken  into 
consideration  far  more  carefully  than  in  the  latter  instrument.  Tempera- 
ture changes  will  affect  the  looseness  in  the  links  thereb}^  destroying  the 
balance  of  the  instrument.    Sudden  changes  are  even  more  injurious. 


INSTRUMENTS 


95 


Changes  in  barometric  pressure  after  the  pilot  has  started  must  be 
taken  into  consideration  and  no  altimeter  yet  has  been  designed  which 
will  do  tliis.  If  during  the  course  of  a  fliiilit  the  aviator  sliouhl  pass  from 
a  region  of  high  barometric  pressure  to  one  of  low  pressure  without 
changing  his  altitude,  he  would  find  that  his  instrument  was  registering 
an  increased  heiglit.  This  is  due,  of  course,  to  atmospheric  conditions,  of 
which  the  aviator  must  be  a  student  in  order  to  be  on  guard  for  such  er- 
rors. Weather  maps  for  the  region  in  which  he  is  operating  will  give  him 
some  idea  of  the  location  of  regions  of  high  or  low  barometric  pressure. 

Another  very  important  error  over  which  the  altimeter  has  no  con- 
trol originates  from  the  topography  of  the  ground  over  which  the  machine 


Fig.  55 — Altimeter  as  used  on  airplanes 


is  flying.  For  the  sake  of  illustration  we  will  assume  that  an  aviator 
leaves  Onmha,  which  has  an  elevation  of  3000  ft.  aI)ove  sea-level,  and 
flies  to  Pike's  Peak.  He  will  set  his  instrument  at  zero  at  Omaha,  and 
on  alighting  on  Pike's  Peak,  which  is  about  14,000  ft.  above  sea-level, 
will  find  that  his  altimeter  reads  in  the  neighborhood  of  11,000  ft.  That 
is,  he  is  11,000  ft.  above  Omaha  but  not  above  Pike's  Peak.  In  other 
words,  the  altimeter  does  not  take  into  consideration  changes  of  elevation 
in  the  territory  over  which  a  plane  flies.  From  this  it  can  l)e  seen  that  a 
thorough  knowledge  of  the  topography  of  the  region  in  wliich  the  pilot 
is  operating  is  verv  essential  in  aerial  Avork. 


96  APPLIED  AERONAUTICS 

There  is  a  fourth  form  of  error  which  is  mechanical  and  is  due  to 
the  lag  of  the  instrument.  It  occurs  especiall}'  in  connection  with  the 
nose  dive,  and  may  be  the  cause  \)f  a  very  serious  accident.  The  aviator 
in  dropping  from  an  altitude  of  10,000  ft.  to  1,000  ft.,  for  instance,  will 
reach  the  lower  elevation  before  his  instrument  can  record  the  change. 
The  danger  lies  in  the  fact  that  if  he  depends  entirely  upon  his  altimeter, 
he  may  not  realize  until  too  late  that  he  is  much  closer  to  the  ground 
than  the  altimeter  indicated.  This  error  will  probably'  never  be  entirely 
eliminated,  but  it  gradually  is  being  reduced  with  increasing  perfection 
in  construction. 

This  practically  covers  the  main  errors  of  the  instrument,  all  of 
which  are  due  to  external  influences.  Mechanical  errors  can  be  detected 
either  by  comparing  the  instrument  with  a  standard  barometer  or  by 
tapping  it  to  discover  slack.  In  fact,  the  instrument  frequently  should 
be  compared  with  a  standard  mercurial  barometer,  merely  as  a  check 
on  its  accuracy. 

It  should  be  added  that  since  hot  air  weighs  less  than  cold  air,  the 
readings  of  an  altimeter  for  the  same  height  will  vary  with  the  tempera- 
ture of  the  air.  Obviously  it  is  impossible  to  obtain  this  temperature  at 
all  times,  hence  this  factor  must  be  neglected,  thus  introducing  an  error 
which  may  reach  as  high  as  ten  per  cent. 

Banking  Meter 

As  its  name  indicates  the  banking  meter,  or  banking  indicator  as  it 
is  sometimes  called,  is  used  to  show  the  amount  of  bank  which  the  pilot 
is  making  and  guard  him  against  skidding  or  side-slipping. 

There  are  two  forms  in  use  at  the  present  time.  One  form  of  this 
meter  is  constructed  on  the  same  principle  as  the  ordinary  spirit  level 
such  as  is  in  use  on  carpenter's  levels,  transits,  etc.  It  consists  essen- 
tially of  a  small  glass  tube  nearly  filled  with  liquid,  leaving  a  small 
bubble.  When  the  tube  and  its  mounting  are  horizontal  the  bubble  will 
come  to  rest  in  the  center  of  the  length  of  the  tube.  Any  slight  inequality 
in  the  surface  beino;  tested  is  sufficient  to  send  the  bubble  to  the  end  of 


Fig.  56 — A  form  of  hanking  meter  patterned  after  the  spirit  level 


INSTRUMENTS 


97 


Fig.  57 — TJir  needle  or  bar,  pirated  in  ihe  eeiiter  ejf  this  hanking  indicator, 
is  actuated  hg  a  plninh  hob  as  the  plane  banks 

the  tube.  Such  an  iiistrnment  would  be  impracticable  in  an  airplane, 
hence  a  cnrved  tube  is  used.  The  fanlt  of  this  instrument  lies  in  the 
fact  that  it  does  not  indicate  the  amount  of  bank  correctly  as  a  rule. 

Tlie  Sperrv  Gyroscope  Co.  has  perfected  a  bankinii  indicator,  an 
illustration  of  which  is  shown  in  Fig.  57.  It  is  based  on  the  principle 
of  the  plumb  bob.  The  upper  framework  shown  on  the  dial  indicates  the 
position  of  the  airplane  relative  to  the  horizontal  and  the  lower  indicator 
(the  horizontal  bar  pivoted  at  its  center)  tells  the  pilot  whether  he  has 
banked  liis  machine  sufficiently  to  meet  the  centrifugal  force  due  to  a 
turn.    The  dials  are  painted  with  radiolite  and  are  visible  at  night. 

The  inclinometer,  which  may  be  used  to  indicate  the  longitudinal 
or  lateral  inclination  of  the  plane,  is  ])ractically  the  same  in  i)rin(iple  as 
the  first  form  of  banking  meter  described  and  merely  serves  as  a  general 
check  on  the  attitude  of  the  machine  in  flight.  Instruments  based  on  the 
]>rinciple  of  the  spirit  level  are  very  inaccurate,  being  subject  to  error 
due  to  acceleration.  Fig.  5(1  is  an  illustration  of  the  airplane  incli- 
nometer.    (See  also  incidence  indicator  and  clinometer.) 

Air  Speed  Indicator 

The  construction  of  this  instrument  is  l>ased  on  the  theory  of  a  i^poed 
measuring  device  known,  after  its  inventor,  as  a  Pitot  tube.  Such  an 
instrument   contains  two  essential   elements;   tlic   first   is  the  dvnamic 


98 


APPLIED   AERONAUTICS 


opeuing  or  mouth  of  the  impact  tube.  (See  Fig.  58.)  It  points  directly 
against  the  current  of  gas  or  liquid  in  which  the  speed  is  to  be  measured 
and  receives  the  full  impact  of  the  current.  The  second  is  a  static  open- 
ing for  obtaining  the  so-called  static  pressure  of  the  moving  fluid,  that 
is,  the  pressure  that  would  be  indicated  by  a  pressure  gauge  moving  with 
the  current  and  not  subject  to  impact.  To  avoid  the  influence  of  impact 
the  static  opening  is  placed  at  right  angles  to  the  dynamic  opening.  If 
the  two  pressure  heads  are  connected  to  the  opening  of  a  U  tube  partly 
filled  with  liquid,  and  a  current  of  air  generated  against  the  mouth  of 
the  impact  tube  it  will  be  seen  that  the  liquid  will  indicate  a  difference 
in  pressure  between  the  two  openings.  Starting  with  the  formula 
V  =  V2gh  where  h  is  the  difference  in  elevation  between  the  levels,  and 
g  the  measure  of  acceleration  due  to  gravity,  a  measurement  can  be  ob- 
tained of  the  velocity  of  the  air  current  by  measuring  the  difference  in 
pressure  between  the  two  openings.  Fig.  58  is  a  cross  section  of  the 
opening  in  a  Pitot  tube.  While  the  dynamic  pressure  can  be  accurately 
determined,  the  static  pressure  is  very  uncertain,  as  the  air  rushing  by 
the  static  opening  is  apt  to  cause  suction.  The  instrument  should  there- 
fore be  calibrated. 


P/tof  Head  Venfun  Meter 

Fig.  58 — Shoiving  operating  principles  of  two  forms  of  air  speed  meters 


Another  form  of  air  speedometer,  also  shown  in  Fig.  58,  is  based  on 
the  principle  of  a  venturi  tube.  This  tube  consists  of  a  short  converging 
inlet  folloAved  by  a  long  diverging  cone.  The  opening  is  placed  at  right 
angles  to  the  air  current  and  a  measurement  is  made  of  the  difference  in 
pressure  existing  between  the  oj)ening  diameter  and  the  smallest  diameter 
of  the  throat.  This  measurement  is  based  on  the  ratio  of  entrance  to 
throat  area,  these  being  the  names  of  the  opening  and  of  the  smallest 
area.  The  tube  is  provided  with  connections  to  a  differential  gauge  by 
which  this  difference  in  pressure  is  measured. 

The  Incidence  Indicator 

The  incidence  indicator,  as  its  name  suggests,  is  used  to  measure  the 
angle  of  attack.  For  this  purpose  an  instrument,  if  possible,  should  be 
"dead  beat,"  or  in  other  words,  free  from  any  tendency  to  swing,  and  it 
must  actually  register  any  change  in  the  direction  of  the  flow  of  air  to 
the  supporting  wings  or  surfaces. 


INSTRUMENTS 


99 


Fig.  59 — Incidence  indivator  mounted  on  one  of  the  forward  struts. 
It  operates  colored  lights  in  the  dial  shoim  in  Fig.  60 

Fig.  59  illustrates  a  form  of  indicator  which  is  attached  to  one  of  the 
forward  struts  of  an  airplane  at  a  point  where  it  will  be  entirely  free 
from  any  influence  of  the  propeller.  AB  is  a  vertical  strut  on  the  air- 
plane, to  which  is  attached  a  wind  vane  CD,  revolving  about  an  axis  EF, 
and  actuating  a  dial  K.  This  wind  vane  CD  is  horizontal  and  always 
points  in  the  direction  of  the  relative  wind,  in  other  words  the  airplane 
revolves  about  the  axis  EF,  as  the  angle  of  attack  changes.  This  device 
is  then  wired  to  an  electric  lamp  box  indicator  similar  to  the  sketch  in 
Fig.  60. 

Fastened  to  the  shaft  EF  (Fig,  59)  is  a  commutator  which  closes 
the  contact  at  certain  points,  and  completes  the  circuit  to  the  different 


Fig.  60 — Indicating  dial  connected  to  incidence  indicator  sthou-n  in  Fig.  59 


100 


APPLIED   AERONAUTICS 


Fuj.  61 — Hitcrrij  clinometer 


lamps  shown  in  Fi.j;.  (>U.  When  the  airplane  is  in  danger  of  stalling  the 
proper  light  flashes  the  information  to  the  pilot.  The  same  is  true  of  the 
other  two  lights. 

The  Sperry  clinometer  is  designed  \\\i\\  the  idea  of  telling  the  pilot 
the  inclination  of  the  axis  of  the  airplane.  Fig.  01  is  an  illustration  of 
such  an  instrument. 

Fig.  02  is  a  cross-section  of  the  same  instrument,  showing  its  con- 
struction, which,  it  will  he  noted,  is  based  on  the  principle  of  the  plund)- 
bol).  The  scale  S  is  mounted  on  the  periphery  of  a  wheel  W,  which  is 
damped  by  floating  in  a  liquid.  The  base  of  the  wheel  has  a  small  weight 
X  to  maintain  it  constantly  in  a  vertical  condition.  There  is  also  an 
expansion  chamber  and  a  filling  screw  similar  to  the  liquid  compass.  It 
is  to  be  noted  that  this  and  similar  instruments  are  subject  to  an  error 
due  to  lag,  caused  by  the  inertia  of  the  wheel  for  an  al)rupt  change  of 
direction.  The  clinometer  is  usually  mounted  in  the  cockpit  where  it 
can  be  seen  at  all  times.  Skillful  pilots  pay  very  little  attention  to  in- 
struments of  this  kind,  however,  relying  almost  entirely  on  instinct. 

The  Automatic  Drift  Set 

Before  explaining  the  operation  of  this  instrument,  it  might  be  well 
to  include  a  word  in  connection  Avith  the  term  "drift,"  as  here  used.  An 
aviator,  desiring  to  fly  to  a  point  due  north  of  his  starting  point,  with  a 
west  wind  blowing,  will  find  at  the  end  of  a  certain  length  of  time  that 
he  is  considerablv  to  the  eastward  of  his  destination,  having  been  blown 


INSTRUMENTS 


101 


from  his  course.  To  .miaid  aiiniiist  this,  two  forms  of  drift  indicators 
are  in  use.  The  first  is  very  simple  and  consists  of  an  eyepiece,  contain- 
inii'  cross-hairs  similar  to  a  surveyor's  transit.  Uy  lookiuii  directly  at  the 
ground,  the  ai>]>ar('nt  motion  of  surface  olijects  can  he  (dtsei'ved  and  made 
to  coincide  with  the  cross-hairs  (»f  the  eyei)iece.  Tliis  is  done  hy  rotating 
the  eyepiece  about  the  axis  of  tlu'  teh'scope,  and  tlie  anuuint  of  this 
rotation,  read  from  a  graduated  circle,  gives  the  drift  angle  directly.  The 
pilot  then  steers  "off  his  course"  an  amount  eijual  to  this  angle  of  drift 
but  in  the  opposite  direction, 

A  more  improved  type  of  this  instrument  is  the  Autonmtic  Drift  Set 
sho^^■n  in  Fig.  03.  As  before,  an  eyepiece  is  used  to  determine  the  angle 
of  drift  as  observed  from  the  apparent  motion  of  objects  on  the  ground. 
As  the  eyepiece  turns  to  coincide  with  this  line  of  motion,  the  connecting- 
cables  shown  turn  the  compass  case,  so  that  the  "lul»l»er  line"  of  the 
compass  is  turned  automatically  in  the  opposite  direction  to  the  drift, 
and  to  an  equal  amount.  The  pilot  then  simply  steers  his  predetermined 
course  on  the  shifted  lubber  line. 

The  Bourdon  Gauge 

This  is  an  instrument  for  measuring  the  pressure  exerted  by  a  gas 
or  liquid,  and  is  the  type  used  in  nearly  all  steam  gauges.  It  is  used  on 
airplanes  for  registering  circulating  oil  pressure,  the  pressure  of  air  in 


Fi(j.  U2 — Cross-section  of  Spcrnj  cliitonietcr 


102 


APPLIED   AERONAUTICS 


F'hi.  63 — ^ perry  Aiitoinatic  Drift  Set^  consisting  of  a  small  revolving 
telescope  which  is  connected  to  compass  case  in  such  a  way  that  compass 
case  icith  luhher  line  is  automatically  turned  to  compensate  for  side  drift 
when  sighting  telescope  is  turned  to  line  up  cross-hairs  u'ith  apparent 
motion  of  plane  over  ground 


I 


INSTRUMENTS 


103 


the  fuel  tank,  etc.  It  depends  for  its  action  upon  the  principle  that  a 
bent  tube  if  subjected  to  internal  pressure  tends  to  straighten  out.  Its 
action  can  be  seen  in  Fig.  64.  A  is  a  tank  of  air  which  can  be  compressed 
to  any  desired  pressure,  as  indicated  by  the  pressure  gauge  C.  D  is  a 
piece  of  rubber  tube  with  the  outer  end  closed,  and  E  is  a  steam  gauge 
from  which  the  dial  and  covering  have  been  removed.  By  opening  the 
valve  V  a  pressure  is  exerted  internally  in  the  rubber  tube  D,  tending  to 
straighten  it  out.     The  same  principle  is  involved  in  the  metal  tube  E 


Fig.  64 — Test  outfit  showing  principle  of  operation  of  Bourdon  gauge 
such  as  used  for  indicating  steam  pressure.  This  principle  is  also  used 
in  radiator  thermometers,  air  and  oil  pressure  gauges,  etc. 


104 


APPLIED  AERONAUTICS 


A      AfoB  full  of  liquid 


Bourdon  Gauge 


Fig.  (Jo — l>>liowiii</  Jioir  a  Bourdon  (jamjp,  connected  to  a  hnlh  half 
fiiU  of  liquid,  is  used  for  a  distance  thermometer.  This  device  is  used  in 
airplanes  for  indicating  radiator  temperatures. 


which  also  tends  to  straighten  out.  This  tube  is  flattened  to  increase  its 
sensitiveness,  and  is  connected  through  a  nuignifying  device  to  the 
pointer,  Avhich  moves  in  front  of  a  graduated  dial. 

The  Radiator  Thermometer 

By  connecting  a  Bourdon  gauge  with  a  tube  of  small  bore  wliich 
ends  In  a  chainber  or  bulb,  and  then  filling  the  system  of  gauge  and  tube 
with  a  liquid  until  the  bulb  becomes  about  half  full  (as  shown  in  Fig.  65) 
a  distance  thermometer  is  obtained,  the  dial  of  which  can  be  placed  at 
a  point  some  distance  away  from  the  controlling  bulb.  This  type  of  gauge 
is  used  to  indicate  the  temperature  of  the  water  in  the  radiator,  so  as  to 
guard  against  overheating  or  freezing. 

As  the  temperature  of  the  radiator,  in  which  the  bulb  is  placed,  rises, 
more  and  more  of  the  liquid  in  the  bulb  will  be  changed  to  vapor,  and  its 
])ressure  will  increase  accordingly  causing  the  pointer  in  the  Bourdon 
gauge  to  move.  By  properly  calibrating  the  dial  the  readings  can  be 
shown  in  degrees  of  temperature  in  i)lace  of  pounds  of  pressure. 


PROPERTIES  OF  VARIOUS  WOODS 


105 


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Chapter  9 

NOMENCLATURE  FOR  AERONAUTICS 

Based  on  official  nomenclature  recommended  by  the  National  Advisory  Committee  for 
Aeronautics  and  definitions  used  and  standardized  by  the  U.  S.  Army  School  of 
Military  Aeronautics  at  Ohio  State  University. 

AERODYNAMICS — The  science  which  treats  of  the  air  or  other  gaseous 
bodies  under  the  action  of  forces  and  of  their  mechanical  effects. 
AEROFOIL — A  thin  wing-Hke  structure,  flat  or  curved,  designed  to  obtain 
reaction  upon  its  surfaces  from  the  air  through  which  it  moves. 
AERONAUTICS — That  branch  of  engineering  Avliich  deals  with  the  design, 
construction  and  operation  of  aircraft. 

AILERON — A  movable  auxiliary  surface  used  for  the  control  of  rolling  mo- 
tion of  an  airplane,  i.  e.,  rotation  about  its  fore  and  aft  axis. 
AIRCRAFT — Any  form  of  craft  designed  for  the  navigation  of  the  air;  air- 
planes, balloons,  dirigibles,  helicopters,  kites,  kite  balloons,  ornithopters,  glid- 
ers, etc.  ;  ;  *«*l^ 
AIRDROME — The  name  usually  applied  to  a  ground  and  buildings  used 
for  aviation. 

AIRPLANE — A  form  of  aircraft  heavier  than  air,  which  has  wing  surfaces 
for  sustentation,  stabilizing  surfaces,  rudders  for  steering,  power  plant  for 
propulsion  through  the  air  and  some  form  of  landing  gear ;  either  a  gear  suit- 
able for  rising  from  or  alighting  on  the  ground,  or  pontoons  or  floats  suitable 
for  alighting  on  or  rising  from  water.  In  the  latter  case,  the  term  "Seaplane" 
is  commonly  used.      (See  definition.) 

Pusher — A  type  of  airplane  with  the  propeller  or  propellers  in  the  rear  of 

the  wings. 

Tractor — A  type  of  airplane  with  the  propeller  or  propellers   in   front 

of  the  wings. 

Monoplane — A  form  of  airplane  whose  main  supporting  surface  is  dis- 
posed as  a  single  wing  extending  equally  on  each  side  of  the  body. 

Biplane — A  form  of  airplane  in  which  the  main  supporting  surface  is 

divided  into  two  parts,  one  above  the  other. 

Triplane^ — A  form  of  airplane  whose  main  supporting  surface  is  divided 

into  three  parts,  superimposed. 


NOMENCLATURE  FOR  AERONAUTICS  107 

Multiplane — An  airplane  the  main  lifting  surface  of  which  consists  of 
numerous  surfaces  or  pairs  of  superimposed  wings. 

One  and  One-Half  Plane — A  biplane  in  which  the  span  of  the  lower 
plane  is  decidedly  shorter  than  that  of  the  upper  plane. 
Flying  Boat — An  airplane  fitted  with  a  boat-like  hull  suitable  for  naviga- 
tion and  arising  from  or  alighting  on  water. 

Seaplane — An  airplane  fitted  with  pontoons  or  floats  suitable  for  alight- 
ing on  or  rising  from  the  water. 
AIR  POCKET — A  local  movement  or  condition  of  the  air  causing  an  airplane 
to  drop  or  lose  its  correct  attitvide. 

AIR  SPEED  METER — An  instrument  designed  to  measure  the  velocity  of 
an  aircraft  with  reference  to  the  air  through  which  it  is  moving. 
ALTIMETER — An  instrument  mounted  on  an  aircraft  to  continuously  indi- 
cate its  height  above  the  surface  of  the  earth. 

ANEMOMETER — An  instrument  for  measuring  the  velocity  of  the  wind  or 
air  currents  with  reference  to  the  earth  or  some  fixed  body. 
ANGLE  OF  ATTACK — The  acute  angle  betvvcen  the  direction  of  relative 
wind  and  the  chord  of  an  aerofoil,  i.  e.,  the  angle  between  the  chord  of  an 
aerofoil  and  its  motion  relative  to  the  air.  (This  definition  may  be  extended 
to  any  body  having  an  axis.) 

Best  Climbing — ^The  angle  of  attack  at  which  an  airplane  ascends  fastest. 
An  angle  about  half  way  between  the  maximum  and  optimum  angle. 
Critical — The  angle  of  attack  at  which  the  lift  is  a  maximum,  or  at  which 
the  lift  curve  has  its  first  maximum ;  sometimes  referred  to  as  the  "burble 
point."  (If  the  lift  curve  has  more  than  one  maximum,  this  refers  to 
the  first  one.) 

Gliding — The  angle  the  flight  path  makes  with  the  horizontal  when 
flying  in  still  air  under  the  influence  of  gravity  alone,  i.  e.,  without  power 
from  the  engine. 

Maximum — The  greatest  angle  of  attack  at  which,  for  a  given  power, 
surface  and  weight,  horizontal  flight  can  be  maintained. 
Minimum — The  smallest  angle  of  attack  at  which,  for  a  given  power, 
surface  and  w^eight,  horizontal  flight  can  be  maintained. 
Optimum — The  angle  of  attack  at  which  the  lift-drift  ratio  is  the  highest. 
ANGLE  OF  INCIDENCE  (Rigger's  Angle)--The  angle  between  the  longi- 
tudinal axis  of  the  airplane  and  the  chord  of  an  aerofoil. 

APPENDIX — The  hose  at  the  bottom  of  a  balloon  used  for  inflation.     In  the 
case  of  a  spherical  balloon  it  also  serves  for  equalization  of  pressure. 
ASPECT  RATIO — The  ratio  of  span  to  chord  of  an  aerofoil. 

AVIATOR — The  operator  or  pilot  of  heavier-than-air  craft.  This  term  is 
applied  regardless  of  the  sex  of  the  operator. 
AVION — Tlie  official  French  term  for  military  airplanes  only. 
AXES  OF  AN  AIRCRAFT— The  three  fixed  lines  of  reference ;  usually  pass- 
ing through  the  center  of  gravity  and  mutually  rectangular.  The  principal 
axis  in  a  fore  and  aft  direction,  usually  parallel  to  the  axis  of  the  propeller  and 
in  the  plane  of  symmetry,  is  the  Longitudinal  Axis  or  the  Fore-and-Aft  Axis. 


108  APPLIED   AERONAUTICS 

The  axis  perpendicular  to  this  and  in  the  plane  of  symmetry  is  the  Vertical 
Axis ;  the  third  axis  perpendicular  to  the  other  two  is  the  Lateral  Axis,  also 
called  the  Transverse  Axis  or  the  Athwartship  i\xis.  In  mathematical  dis- 
cussion the  first  of  these  axes,  drawn  from  front  to  rear  is  called  the  X  Axis ; 
the  second.  dra\\  n  upward ;  the  Z  Axis  ;  and  the  third,  forming  a  "left-handed" 
system,  the  Y  Axis. 

BALANCED  CONTROL  SURFACE— A  type  of  surface  secured  by  adding 
area  forward  of  the  axis  of  rotation.     In  an  airstream  a  force  is  exerted  on  this 
added  area,  tending  to  aid  in  the  movement  about  the  axis. 
BALANCING  FLAPS— (See  AILERON.) 

BALLONET — A  small  balloon  within  the  interior  of  a  balloon  or  dirigible 
for  the  purpose  of  controlling  the  ascent  or  descent,  and  for  maintaining  pres- 
sure on  the  outer  envelope  so  as  to  prevent  deformation.  The  ballonet  is  kept 
inflated  with  air  at  the  required  pressure,  under  the  control  of  a  blower  and 
valves. 

BALLOON — A  form  of  aircraft  comprising  a  gas  bag  and  a  basket  and  sup- 
ported in  the  air  by  the  buoyancy  of  the  gas  contained  in  the  gas  bag,  which 
is  lighter  than  the  amount  of  air  it  displaces ;  the  form  of  the  gas  bag  is  main- 
tained by  the  pressure  of  the  contained  gas. 

Barrage — A  small  spherical  captive  balloon,  raised  as  a  protection 
against  attacks  by  airplanes. 

Captive — A  balloon  restrained  from  free  flight  by  means  of  a  cable  at- 
taching it  to  the  earth. 

Kite — An  elongated  form  of  captive  balloon,  fitted  with  tail  appendages 
to  keep  it  headed  into  the  wind,  and  deriving  increased  lift  due  to  its  axis 
being  inclined  to  the  wind. 

Pilot — A  small  spherical  balloon  sent  up  to  show  the  direction  of  the 
wind. 

Sounding — A  small  spherical  balloon  sent  aloft,  without  passengers,  but 
with  registering  meterological  instruments  for  recording  atmospheric 
conditions  at  high  altitudes. 
BALLOON— DIRIGIBLE— A  form  of  balloon  the  outer  envelope  of  which 
is  of  elongated  horizontal  form,  provided  with  a  car,  propelling  system,  rud- 
ders and  stabilizing  surfaces.  Dirigibles  are  divided  into  three  classes :  Rigid, 
Semi-rigid  and  Non-rigid.  In  the  Rigid  type  the  outer  covering  is  held  in 
place  and  form  by  a  rigid  internal  frame  work  and  the  shape  is  maintained  in- 
dependently of  the  contained  gas.  The  shape  and  form  of  the  Semi-rigid  type 
is  maintained  partly  by  an  inner  framework  and  partly  by  the  contained  gas. 
The  Non-rigid  type  is  held  to  form  entirely  by  the  pressure  of  the  con- 
tained   gas. 

BALLOON  BED — A  mooring  place  on  the  ground  for  a  cai)tiv,e  balloon. 
BALLOON   CLOTH— The  cloth,  usually  cotton,  of  which   balloon   fabrics 
are  made. 

BALLOON  FABRIC— The  finished  material,  usually  rubberized,  of  which 
balloon  envelopes  are  made. 


NOMENCLATURE   FOR   AERONAUTICS  109 

BANK — To  incline  an  airplane  laterally,  i.  e.,  to  rotate  it  abont  the  fore-and- 
aft  axis  when  making  a  turn.  Right  bank  is  to  incline  the  air])lane  with  the 
right  wing  down.  Also  used  as  a  noun  to  describe  the  position  of  an  airplane 
when  its  lateral  axis  is  inclined  to  the  horizontal. 

BAROGRAPH — An  instrument  for  recording  variations  in  barometric  pres- 
sure. In  aeronautics  the  charts  on  which  the  records  are  made  are  prepared 
to  indicate  altitudes  directly  instead  of  barometric  pressure,  inasmuch  as  the 
atmospheric  pressure  \aries  almost  directly  with  the  altitude. 
BAROMETER — An  instrument  for  measuring  the  pressure  of  the  atmos- 
phere. 

BASKET — The  car  suspended  beneath  the  balloon  for  passengers,  ballast,  etc. 
BIPLANE— (See  AIRPLANE.) 

BODY  (OF  AN  AIRPLANE)— A  structure,  usually  enclosed,  which  contains 
in  a  streamline  housing  the  power  plant,  fuel,  passengers,  etc. 

Fuselage — A  type  of  body  of  streamline  shape  carrying  the  empannage 
and  usually  forming  the  main  structural  unit  of  an  airplane. 
Monocoque — A  special  type  of  fuselage  constructed  of  metal  sheeting  or 
laminated  wood.   A  monocoque  is  generally  of  circular  or  elliptical  cross- 
section. 

Nacelle — A  type  of  body  shorter  than  a  fuselage.     It  does  not  carry  the 
empannage,  but  acts  more  as  a  streamline  housing.    Usually  used  on  a 
pusher  type  of  machine. 

Hull — A  boat-like  structure  which  forms  the  body  of  a  flying-boat. 
BONNET — The  appliance,  having  the  form  of  a  parasol,  which  protects  the 
valve  of  a  spherical  balloon  against  rain. 
BOOM— (See  OUTRIGGER.) 

BOWDEN  WIRE — A  stiff  control  wire  enclosed  in  a  tube  used  for  light  con- 
trol work  where  the  strain  is  comparatively  light,  as  for  instance  throttle  and 
spark  controls,  etc. 

BOWDEN  WIRE  GUIDE— A  close  wound,  spring-like,  flexible  guide  for 
Bowden  wire  controls. 

BRIDLED — The  system  of  attachment  of  cables  to  a  balloon,  including  lines 
to  the  suspension  band. 

BULLS  EYES — Small  rings  of  wood,  metal,  etc.,   forming  i)art  of  balloon 
rigging,  used  for  connection  or  adjustment  of  ropes. 
BURBLE  POINT— (See  ANGLE— CRITICAL. ) 

CABANE  (OR  CABANE  STRUT)— In  a  monoplane,  the  strut  or  pyramidal 
frame  work  projecting  above  the  body  and  wings  and  to  which  the  stays, 
ground  wires,  braces,  etc.,  for  the  wing  are  attached. 

In  a  biplane,  the  compression  member  of  an  auxiliary  truss,  serving  to 
support  the  overhang  of  the  upper  wing. 

CAMBER — The  convexity  or  rise  of  the  curve  of  an  aerofoil  from  its  chord, 
usually  expressed  as  the  ratio  of  the  maximum  departure  of  the  curve  from 
the  chord  as  a  fraction  thereof.  Top  Camber  refers  to  the  top  surface  and 
Bottom  Camber  to  the  bottom  surface  of  an  aerofoil.  Mean  Camber  is  the 
mean  of  these  two. 


no  APPLIED   AERONAUTICS 

CAPACITY-CARRYING— The  excess  of  the  total  lifting  capacity  over  the 
dead  load  of  an  aircraft.  The  latter  includes  structure,  power  plant  and  essen- 
tial accessories.     Gasoline  and  oil  are  not  considered  essential  accessories. 

The  cubic  contents  of  a  balloon. 
CAPACITY-LIFTING— (See    LOAD)— The    maximum    flying   load    of   an 
aircraft. 

CATHEDRAL — A  negative  dihedral. 

CEILING — The  maximum  possible  altitude  to  which  a  given  airplane  can 
climb. 

CENTER — The  point  in  which  a  set  of  effects  is  assumed  to  be  accumulated, 
producing  the  same  effect  as  if  all  were  centered  at  this  point. 

There  are  five  main  centers  in  an  airplane— Center  of  Lift,  Center  of 
Gravity,  Center  of  Thrust,  Center  of  Drag  and  Center  of  Keelplane  Area. 
The  latter  is  also  called  the  Directional  Center.  The  stability,  controllability 
and  general  air  worthiness  of  an  airplane  depend  largely  on  the  proper  posi- 
tioning of  these  centers. 

CENTER  OF  PRESSURE  OF  AN  AEROFOIL— The  point  in  the  plane 
of  the  chords  of  an  aerofoil,  prolonged  if  necessary,  through  which  at  any 
given  attitude  the  line  of  action  of  the  resultant  air  force  passes.  (This  defi- 
nition may  be  extended  to  any  body.) 

CENTER  PANEL — The  central  part  of  the  upper  wing  (of  a  biplane)  above 
the  fuselage.     The  upper  wings  are  attached  to  this  on  either  side. 
CHORD — (Of  an  aerofoil  section.)      A  straight  line  tangent   to   the   under 
curve  of  the  aerofoil  section,  front  and  rear. 

CHORD  LENGTH— (Or  length  of  Chord.)— The  length  of  an  aerofoil  sec- 
tion projected  on  the  chord,  extended  if  necessary. 
CLINOMETER— (See  INCLINOMETER.) 

CLOCHE — The  bell-shaped  construction  which  forms  the  lower  part  of  the 
pilot's  control  lever  in  the  Bleriot  control  and  to  which  the  control  cables  are 
attached. 

COCKPIT — The  space  in  an  aircraft  body  occupied  by  pilots  or  passengers. 
CONCENTRATION  RING— The  hoop  to  which  are  attached  the  ropes  sus- 
pending the  basket  (of  a  balloon). 

CONTROLS — A  general  term  applied  to  the  mechanism  used  to  control  the 
speed,  direction  of  flight  and  altitude  of  an  aircraft. 

Bridge  (Deperdussin-"Dep"  Control) — An  inverted  "U"  frame  pivoted 
near  its  lower  points,  by  wdiich  the  motion  of  the  elevators  is  controlled. 
The  ailerons  are  controlled  by  a  wheel  mounted  on  the  upper  center  of 
this  bridge. 

Dual — Two  sets  of  inter-connected  controls  allowing  the  machine  to  be 
operated  by  one  or  two  pilots. 

Shoulder — A  yoke  fitting  around  the  shoulders  of  the  pilot  by  means  of 
which  the  ailerons  are  operated  (by  the  natural  side  movement  of  the 
pilot's  body)  to  cause  the  proper  amount  of  banking  when  making  a 
turn  or  to  correct  excessive  bank.  (Used  on  early  Curtiss  planes.) 
Stick  (Joy-stick) — A  vertical  lever  pivoted  near  its  lower  end  and  used 
to  operate  the  elevators  and  ailerons. 


NOMENCLATURE    FOR   AERONAUTICS  111 

COWLS — The  metal  covering  enclosing  the  engine  section  of  the  fuselage. 
CROW'S  FOOT — A  system  of  diverging  short  ropes  for  distributing  the  pull 
of  a  single  rope.     (Used  principally  on  balloon  nets.) 

DECALAGE — The  difference  in  the  angular  setting  of  the  chord  of  the  upper 
wing  of  a  biplane  with  reference  to  the  chord  of  the  lower  wing. 
DIHEDRAL  (In  an  airplane) — The  angle  included  at  the  intersection  of  the 
imaginary  surfaces  containing  the  chords  of  the  right  and  left  wings  (con- 
tinued to  the  plane  of  symmetry  if  necessary).  This  angle  is  measured  in  a 
plane  perpendicular  to  that  intersection.  The  measure  of  the  dihedral  is  taken 
as  90  deg.  minus  one-half  of  this  angle  as  defined. 

The  dihedral  of  the  upper  wing  may  and  frequently  does  differ  from  that 
of  the  lower  wing  in  a  biplane. 

Lateral — An  airplane  is  said  to  have  lateral  dihedral  when  the  wings 
slope  downward  from  the  tips  toward  the  fuselage. 

Longitudinal — The  angular  difference  between  the  angle  of  incidence  of 
the  main  planes  and  the  angle  of  incidence  of  the  horizontal  stabilizer. 
DIRIGIBLE — A  form  of  balloon,  the  outer  envelope  of  which  is  of  elongated 
horizontal  form,  provided  with  a  propelling  system,  car,  rudders  and  stabil- 
izing surfaces. 

Non-Rigid — A  dirigible  whose  form  is  maintained  by  the  pressure  of  the 
contained  gas  assisted  by  the  car  suspension  system. 
Rigid — A  dirigible  whose  form  is  maintained  by  a  rigid  structure  con- 
tained within  the  envelope. 

Semi-Rigid — -A  dirigible  whose  form  is  maintained  by  means  of  a  rigid 
keel  and  by  gas  pressure. 

DIVING  RUDDER— (See  ELEVATOR.) 

DOPE — A  preparation,  the  base  of  which  is  cellulose  acetate  or  cellulose 
nitrate,  used  for  treating  the  cloth  surfaces  of  airplane  members  or  the  fabric 
of  balloon  gas  bags.  It  increases  the  strength  of  the  fabric,  produces  taut- 
ness,  and  acts  as  a  filler  to  make  the  fabric  impervious  to  air  and  moisture. 
DRAG — The  component  parallel  to  the  relative  wind  of  the  total  force  on  an 
aircraft  due  to  the  air  through  which  it  moves. 

That  part  of  the  drag  due  to  the  wings  is  called  "Wing  Resistance" 
(formerly  called  "Drift")  ;  that  due  to  the  rest  of  the  airplane  is  called  "Para- 
site Resistance"  (formerly  called  head  resistance). 

The  total  resistance  to  motion  through  the  air  of  an  aircraft,  that  is.  the 
sum  of  the  drift  and  parasite  resistance.    Total  Resistance. 
DRIFT — The  component  of  the  resultant  wind  pressure  on  an  aerofoil  or 
wing  surface  parallel  to  the  air  stream  attacking  the  surface. 

Also  used  as  synonymous  with  lee-way. 
(See  DRAG.) 
DRIFT  INDICATOR — An  instrument  for  the  measurement  of  the  angular 
deviation  of  an  aircraft  from  a  set  course,  due  to  cross  winds. 

Also  called  Drift  Meter. 
DRIFT  WIRES— Wires  which  take  the  drift  load  and  transfer  it  through 
various  members  to  the  body  of  the  airplane. 


112  APPLIED   AERONAUTICS 

DRIP  CLOTH — A  curtain  around  the  equator  of  a  balloc^n  wliich  prevents 

rain  from  dripping  into  the  basket. 

DROOP— 

(a)  An  aileron  is  said  to  have  droop  when  it  is  so  adjusted  that  its  trailing 
edge  is  below  the  trailing  edge  of  the  main  plane. 

(b)  When  a  wing  is  warped  to  give  wash-out  or  wash-in.  its  trailing 
edge  will,  relative  to  the  leading  edge,  be  displaced  progressively  from 
one  end  to  the  other.     A  downward  displacement  is  called  droop. 

ELEVATOR — A  hinged  surface,  usually  in  the  form  of  a  horizontal  rudder, 
mounted  at  the  tail  of  an  aircraft  for  controlling  the  longitudinal  attitude  of 
the  aircraft,  i.  e.,  its  rotation  abovit  the  lateral  axis. 
EMPANNAGE — A  term  applied  to  the  tail  group  of  parts  of  an  airplane. 

(See  TAIL.) 
ENGINE  SILL,  BEARERS,  SUPPORTS— The  members  forming  the  en- 
gine bed. 

ENTERING  EDGE — The  foremost  part  or  forward  edge  of  an  aerofoil  or 
propeller  blade. 

ENVELOPE — The  portion  of  the  balloon  or  dirigible  which  contains  the  gas. 
EQUATOR — The  largest  horizontal  circle  of  a  spherical  balloon. 
FAIRING — A  wood  or  metal  form  attached  to  the  rear  of  struts,  braces  or 
wires  to  give  them  a  streamline  shape. 
FAIR  LEAD— A  guide  for  a  cable. 

FIN — A  small  fixed  aerofoil  attached  to  part  of  an  aircraft  to  promote  stabil- 
ity; for  example,  tail  fin,  skid  fin,  etc.  Fins  may  be  either  horizontal  or  ver- 
tical and  are  often  adjustable. 

(See  STABILIZER.) 
FIRE  DASH — A  metal  screen  dividing  the  engine  section  of  an  airplane  body 
from  the  cockpit  section. 

FLIGHT  PATH — The  path  of  the  center  of  gravity  of  an  aircraft  with  ref- 
erence to  the  earth. 

FLOAT — That   portion  of  the   landing  gear  of  an   aircraft   which   provides 
buoyancy  when  it  is  resting  on  the  surface  of  the  water. 
FLYING  BOAT— (See  AIRPLANE.) 

FLYING  POSITION — The  position  of  a  machine,  assumed  when  flying 
horizontally  in  still  air.  When  on  the  ground  the  machine  is  placed  in  a  fly- 
ing position  by  leveling  both  longitudinally  and  laterally.  The  two  longerons, 
engine  sills  or  other  perpendicular  parts  designated  by  the  maker  are  taken 
as  reference  points  from  which  to  level. 
FOOT  BAR— (See  RUDDER  BAR.) 
FUSELAGE— (See  BODY.) 

FUSELAGE  COVER — A  cover  placed  on  a  fuselage  to  preserve  a  streamline 
shape. 

GAP — The  shortest  distance  between  the  planes  of  the  chords  of  the  upper 
and  lower  wings  of  a  biplane. 
GAS  BAG— (See  ENVELOPE.) 
GLIDE — To  fly  without  power  and  under  the  influence  of  gravity  alone. 


NOMENCLATURE   FOR   AERONAUTICS  113 

GLIDER— A  form  of  aircraft  similar  to  an  airplane  but  without  any  power 
plant. 

When  utilized  in  variable  winds  it  makes  use  of  the  soaring  principles 
of  flight  and  is  sometimes  called  a  soaring-  machine. 
GLIDING  ANGLE— (See  ANGLE.) 

GORE — ( )ne  of  the  segments  of  fabric  comprising  the  envelope  of  a  balloon. 
GROUND  CLOTH — Canvas  placed  on  the  ground  to  protect  a  balloon. 
GUIDE  ROPE — A  long  trailing  rope  attached  to  a  spherical  balloon  or  diri- 
gible to  serve  as  a  brake  and  as  a  variable  ballast. 

GUY — A  rope,  chain,  wire  or  rod  attached  to  an  (.>bject  to  guide  or  steady- 
it,  such  as  guys  to  wing,  tail  or  landing  gear. 
HANGAR — An  airplane  shed. 

HEAD  RESISTANCE— (See  PARASITE  RESISTANCE.) 
HELICOPTER — A  form  of  aircraft  whose  supi)ort  in  the  air  is  derived  from 
the  vertical  thrust  of  propellers. 

HORN-CONTROL  ARM— An  arm  at  right  angles  to  a  control  surface  to 
which  a  control  cable  is  attached,  for  example,  aileron  horn,   rudder  horn, 
elevator  horn,  etc.     More  commonly  called  a  Mast. 
HULL— (See  BODY.) 

INCLINOMETER — An  instrument  for  measuring  the  angle  made  by  the 
axis  of  an  aircraft  with  the  horizontal. 

Indicator-Banking — An  inclinometer  indicating  lateral  inclination  or 
bank. 
INSPECTION  WINDOW — A  small  transparent  window  in  the  envelope 
of  a  balloon  or  in  the  wing  of  an  airplane  to  allow  inspection  of  the  interior, 
or  of  aileron  controls  when  the  latter  are  mounted  inside  an  aerofoil  section. 
INSTABILITY — An  inherent  condition  of  a  body,  which,  if  the  body  is  dis- 
tributed, causes  it  to  move  toward  a  position  away  from  its  first  position, 
instead  of  returning  to  a  condition  of  equilibrium. 

KEEL  PLANE  AREA — The  total  effective  area  of  an  aircraft  which  acts  to 
prevent  skidding  or  side  slipping. 

KITE — A  form  of  aircraft  without  other  propelling  means  than  the  tow-line 
pull,  whose  support  is  derived  from  the  force  of  the  wind  moving  past  its 
surfaces. 

LANDING  GEAR — The  understructure  of  an  aircraft  designed  to  carry  the 
load  when  resting  on,  or  running  on,  the  surface  of  the  land  or  water. 
LEADING  EDGE— (See  ENTERING  EDGE.) 

LEEWAY — The  angle  of  deviation  from  a  set  course  over  the  earth,  due  to 
cross  currents  of  wind.    Also  called  Drift. 

LIFT — The  component  of  the  force  due  to  the  air  pressure  of  an  aerofoil  re- 
solved perpendicular  to  the  flight  path  in  a  vertical  plane. 
LIFT-DRIFT  RATIO— The  proportion  of  lift  to  drift  is  known  as  the  lift- 
drift  ratio.     It  expresses  the  efficiency  of  the  aerofoil. 
LIFT  BRACING— (See  STAY.) 
LOAD— 

Dead — The  structure,  power  plant  and  essential  accessories  of  an  air- 
craft. 


114  APPLIED   AERONAUTICS 

Full — The   maximum    weight   which   an   aircraft   can    support   in    flight; 

the  gross  weight. 

Useful— "J  he  excess  of  the  full  load  over  the  dead  weight  of  the  aircraft 

itself,  i.  e.,  over  the  weight  of  its  structure,  power  plant  and  essential 

accessories.     (These  last  must  be  specified.) 

(See  Capacity.) 
LOADING — The  weight  carried  by  an  aerofoil,  usually  expressed  in  pounds 
per  square  foot  of  superficial  area. 

LOBES — Bags  at  the  stern  of  an  elongated  balloon  designed  to  give  it  direc- 
tional stability. 

LONGERON — The  principal  fore-and-aft  structural  members  of  the  fuselage 
or  nacelle  of  an  air])lane. 

(See  LONGITUDINAL.) 
LONGITUDINAL — A  fore-and-aft  member  of  the  framing  of  an  airplane 
body,  or  of  the  float  in  a  seaplane,  usually  continuous  across  a  number  of 
points  of  support. 

LONGITUDINAL  DIHEDRAL— (See  DIHEDRAL.) 
MAST— (See  HORN.) 
MONOCOQUE— (See  BODY.) 

MONOPLANE — A  form  of  airplane  whose  main  supporting  surface  is  a  single 
wing  extending  equally  on  each  side  of  the  body. 

(See  AIRPLANE.) 
MOORING  BAND — The  1:)and  of  tape  over  the  top  of  a  balloon  to  which  are 
attached  the  mooring  ropes. 
NACELLE— (See  BODY.) 

NET — A  rigging  made  of  ropes  and  twine  on  spherical  balloons,  which  sup- 
ports the  entire  load  carried. 

NOSE  DIVE — A  dangerously  steep  descent,  head  on. 

NOSE  PLATE — A  plate  at  the  nose  or  front  end  of  the  fuselage  in  which 
the  longerons  terminate. 

NOSE  SPIN — A  nose  dive  in  which  the  airplane  rotates  about  its  own  axis 
due  to  the  reaction  from  the  propeller.  It  usually  results  from  failure  to  shut 
off  the  engine  in  time  when  going  into  a  nose  dive,  and  is  likely  to  cause 
complete  loss  of  control. 

ORNITHOPTER — A  form  of  aircraft  deriving  its  support  and  propelling 
force  from  flapping  wings. 

OUT-RIGGER — -Members,  independent  of  the  body,   extending  forward  or 

to  the  rear  and  supporting  control  or  stabilizing  surfaces. 

OVERHANG — The  distance  the  wings  project  out  beyond  the  outer  struts. 

PAN  CAKE,  TO — To  descend  as  a  parachute  after  a  machine  has  lost  for- 
ward velocity.  To  strike  the  ground  violently  without  much  forward  "motion. 
PANEL — A  portion  of  a  framed  structure  between  adjacent  posts  or  struts. 
Applied  to  the  fuselage  it  is  the  area  bounded  by  two  struts  and  the  longerons. 
An  entire  wing  is  often  spoken  of  as  a  panel.  Thus  the  upper  lifting  surface 
of  a  biplane  is  usually  of  three  parts  designated  as  the  right  upper  panel,  left 
upper  panel  and  the  center  panel. 


NOMENCLATURE    FOR   AERONAUTICS  115 

PARACHUTE — An    a|)])aralus    made    like    an    nnihrclla    used    to    retard    the 
ilescent  of  a  fallini;'  Ixxlw 

PARASITE  RESISTANCE— 'Ihe  total  resistance  to  motion  through  the  air 

of  all  parts  of  an  aircraft  not  a  j)art  of  the  main  lifting-  surface. 

PATCH  SYSTEM — A  system  of  construction  in  which  patches  or  adhesive 

tlaps  are  use<l  in  place  of  the  suspension  band  in  a  balloon. 

PERMEABILITY — The  measure  of  the  loss  of  gas  by  diffusion  through  the 

intact  l)alloon  fabric. 

PHILLIPS  ENTRY — A  reverse  curve  on  the  lower  surface  of  an  aerofoil, 

towards  the  entering  L'd^t:,  designed  to  more  evenly  divide  the  air. 

PITCH-OF  A  PROPELLER— (See  PROPELLER.) 

PITCH-OF  A  SCREW — The  distance  a  screw  advances  in   its  nut  in   one 

rex'olution. 

PITCH,  TO — To  ])lunge  in  a  fore-and-aft  directittn. 

PITOT  TUBE — A  tube  with  an  end  open  sciuare  to  the  fluid  stream,  used  as  a 

detector  of  an  impact  pressure.     It  is  usually  associated  with  a  concentric 

tube  surrounding  it,  having  perforations  normal  to  the  axis  for   indicating 

static  pressure ;  or  there  is  such  a  tube  placed  near  it  and  parallel  to  it,  with  a 

closed  conical  end  and  having  perforations  in  its  side.     The  velocity  of  the 

fluid  can  be  determined  from  the  difference  between  the  impact  pressure  and 

the  static  pressure,  as  read  by  a  suitable  gauge.     This  instrument  is  often 

used  to  determine  the  velocity  of  an  aircraft  through  the  air. 

PLANE  OF  SYMMETRY— A  vertical  plane  through  the  longitudinal  axis 

of  an  airi)lane.     It  divides  the  airplane  into  two  symmetrical  portions. 

PONTOON-  (See  FLOAT.) 

PROPELLER  OR  AIR  SCREW— A  body  so  shaped  that  its  rotation  about 

an  axis  produces  a  thrust  in  the  direction  of  its  axis. 

Disc-Area  of  Propeller — The  total  area  of  a  circle  swept  by  the  propeller 
tips. 

Pitch  Of — The  distance  a  propeller  will  advance  in  one  revolution,  sup- 
posing the  air  to  be  solid. 

Race — The  stream  of  air  driven  aft  by  the  pro{)eller  and  with  a  velocity 
relative  to  the  airi)lane  greater  than  tliat  of  the  surrounding  body  of 
still  air.      (Frequently  called  slip-stream.) 

Slip  Of — The  difference  between  the  distance  a  propeller  actually  ad- 
vances and  the  distance  it  would  advance  while  making  the  same  number 
of  revolutions  in  a  solid  medium.  Usually  expressed  as  a  percentage 
of  the  total  distance. 

Torque  Of — The  turning  moment  of  the  propeller.     The  effect  of  pro- 
peller torque  is  an  equal  reaction  tending  to  rotate  the  \vhole  airplane 
in  the  opposite  direction  to  that  of  the  propeller. 
PUSHER— (See  AIRPLANE.) 

PYLON — A  post,  mast  or  pillar  serving  as  a  marker  of  a  flying  course.  Also 
used  infrequently  to  designate  the  control  masts  such  as  the  aileron  mast, 
rudder  mast,  elevator  mast,  etc. 


116  APPLIED   AERONAUTICS 

RAKE — The  angular  deviation  of  the  outer  end  of  a  wing  from  a  line  at  right 
angles  to  the  entering  edge. 

RELATIVE  WIND — The  motion  of  the  air  with  reference  to  a  moving  body. 
Its  direction  and  velocity,  therefore,  are  found  by  adding  two  vectors,  one 
being  the  velocity  of  the  air  with  reference  to  the  earth,  the  other  being  equal 
and  opposite  to  the  velocity  of  the  body  with  reference  to  the  earth. 

RETREAT— (See  SWEEP  BACK.) 

RIB — A  member  used  to  give  strength  and  shape  to  an  aerofoil  in  a  fore- 
and-aft  direction. 

Web — A   light   rib,   the   central   part   of   which   is   cut   out   in   order   to 
lighten  it. 

Compression — A  rib  heavier  than  the  w^eb  type  and  so  constructed  as  to 
resist  the  compression  due  to  the  wire  bracing  of  the  airplane. 
Secondary  Nose— Small  ribs  extending  from  the  front  sj^ar  to  the  nose 
strip  (entering  edge).  Placed  between  the  main  ribs  to  give  support 
to  the  fabric  near  the  entering  edge.  Sometimes  called  Stub  Ribs. 
RIGGING — The  art  of  truing  up  an  airplane  and  keeping  it  in  flying  con- 
dition. 

RIP  CORD — The  rope  running  from  the  rip  panel  of  a  balloon  to  the  basket, 
the  pulling  of  which  causes  immediate  deflation. 

RIP  PANEL — -A  strip  in  the  upper  part  of  a  ballooii  which  is  torn  off  when 
immediate  deflation  is  desired. 

RUDDER — A  hinged  or  pivoted  surface,  usually  more  or  less  flat  or  stream- 
lined, used  for  the  purpose  of  controlling  the  attitude  of  an  aircraft  about  its 
vertical  axis,  i.  e.,  for  controlling  its  lateral  movement. 

RUDDER  BAR — A  bar  pivoted  at  the  center,  to  the  ends  of  which  the  rud- 
der control  cables  are  attached.  The  pilot  operates  the  rudder  by  moving  the 
rudder  bar  with  his  feet. 

RUDDER  POST — The  post  to  which  the  rudder  is  hinged,  generally  forming 
the  rear  vertical  member  of  the  vertical  stabilizer. 

SEA  PLANE — An  airplane  fitted  with  pontoons  or  floats  suitable  for  alight- 
ing on  or  rising  from  the  water. 
(See  AIRPLANE.) 

SERPENT — A  short  heavy  guide  rope  used  with  balloons. 
SERVING — A  binding  of  wire,  cord  or  other  material.     Usually  used  in  con- 
nection with  joints  in  wood,  and  cable  splices. 

SIDE  SLIPPING — Sliding  sideways  and  downward  toward  the  center  of  a 
turn,  due  to  an  excessive  amount  of  bank.     It  is  the  opposite  of  skidding. 
SIDE  WALK — A  reinforced  portion  of  the  wings  near  the  fuselage  serving 
as  a  support  in  climbing  about  the  air])lane.     Otherwise  known  as  running 
board. 

SKIDDING — Sliding  sideways  away  from  the  center  of  a  turn,  due  to  an  in- 
sufficient amount  of  bank.     It  is  the  opposite  of  side  slipping. 


NOMENCLATURE  FOR  AERONAUTICS  117 

SKIDS-LANDING  GEAR — Long  wooden  or  nKtal  runners  designed  to  pre- 
vent nosing  of  a  land  machine  when  landing,  or  to  prevent  dropping  into 
holes  or  ditches  in  rough  ground.  Generally  designed  to  function  in  case  the 
wheels  should  collapse  or  fail  to  act. 

Tail — A  skid  supporting  the  tail  of  a  fuselage  while  on  the  ground. 
Wing — A  light  skid  placed   under  the   lower  wing  to  i)revent   possible 
damage  on  landing. 
SKIN  FRICTION — Friction  between  the  air  and  a  surface  over  which  it  is 
passing 

SLIP  STREAM— (See  PROPELLER  RACE.) 
SOARING  MACHINE— (See  GLIDER.) 
SPAN-WING — .Span  is  the  dimension  of  a  surface  across  the  air  stream. 

Wing   Span  or  Spread  of  a  machine  is  length  overall   from  tip  to  tip 
of  wings. 
SPARS-WING — Long  pieces  of  wood  or  other  material  forming  the  main 
supporting  members  of  the  wing,  and  to  which  the  ribs  are  attached. 
SPREAD— (See  SPAN.) 

STABILITY — The  cjuality  of  an  aircraft  in  flight  wdiich  causes  it  to  return 
to  a  condition  of  equilibrium  after  meeting  a  disturbance. 

Directional — That  property  of  an  airplane  by  virtue  of  which  it  tends  to 
hold  a  straight  course.  That  is,  if  a  machine  tends  constantly  to  veer  off 
its  course  necessitating  exercise  of  the  controls  by  the  pilot  to  keep  it  on 
its  course,  it  is  said  to  lack  directional  stability. 

Dynamical — The  ciuality  of  an  aircraft  in  flight  which  causes  it  to  return 
to  a  condition  of  ecjuilibrium  after  its  attitude  has  been  changed  by  meet- 
ing some  disturbance,  e.  g.,  a  gust.  This  return  to  equilibrium  is  due  to 
two  factors  ;  first,  the  inherent  righting  moments  of  the  structure  ;  second, 
the  damping  of  the  oscillations  by  the  tail,  etc. 

Inherent — Stability  of  an  aircraft  due  to  the  disposition  and  arrangement 
of  its  fixed  parts,  i.  e.,  that  property  which  causes  it  to  return  to  its  nor- 
mal attitude  of  flight  without  the  use  of  the  controls. 

Lateral — The  property  of  an  airplane  by  virtue  of  which  the  lateral  axis 
tends  to  return  to  a  horizontal  position  after  meeting  a  disturbance. 
Longitudinal — An  airplane  is  longitudinally  stable  wdien  it  tends  to  fly 
on  an  even  keel  without  pitching  or  plunging. 

Statical — In  wind  tunnel  experiments  it  is  found  that  there  is  a  definite 
angle  of  attack  such  that  for  a  greater  angle  or  a  less  one  the  righting 
moments  are  in  such  a  sense  as  to  tend  to  make  the  attitude  return  to 
this  angle.  This  holds  true  for  a  certain  range  of  angles  on  each  side  of 
this  definite  angle  ;  and  the  machine  is  said  to  possess  "statical  stability" 
through  this  range. 
STABILIZER — Balancing  planes  of  an  aircraft  to  promote  stability. 

Horizontal — A  horizontal  fixed  plane  in  the  empannage  designed  to  give 

stability  about  the  lateral  axis. 

Vertical — A  vertical  fixed  plane  in  the  enii)annage  to  promote  stability 

about  the  vertical  axis. 

Mechanical — Any  mechanical  device  designed  to  secure  stability  in  flight. 


118  APPLIED   AERONAUTICS 

STABILIZING  FINS — Vertical  surfaces  mounted  longitudinally  between 
planes,  to  increase  the  keel  plane  area. 

STAGGER — The  amount  of  advan.cc  of  the  entering  edge  of  a  superposed 
aerofoil  of  an  airplane,  over  that  of  a  lower,  expressed  as  a  percentage  of  the 
gap.     It  is  considered  positive  when  the  upper  aerofoil  is  forward. 
STALLING — A  term  describing  the  condition  of  an  airplane  which,  from  any 
cause  has  lost  the  relative  speed  necessary  for  steerageway  and  control. 
STATION — The  points  at  which  struts  join  the  longerons  in  a  fuselage,  are 
termed  stations  and  are  numbered  according  to  some  arbitrary  system.    Some 
makers  begin  with  No.  1  at  the  nose  plate  and  number  toward  the  rear.    Other 
makers  begin  with  0  at  the  tail  post  and  number  toward  the  front. 
STATOSCOPE — An  instrument  to  detect  the  existence  of  a  small  rate  of 
ascent  or  descent,  principally  used  in  ballooning. 

STAY— A  wire,  rope,  or  the  like  used  as  a  tie  piece  to  hold  parts  together,  or 
to  contribute  stiffness  ;  for  example,  the  stays  of  the  wing  and  body  trussing. 
STREAMLINE-FLOW — A  term  used  to  describe  the  condition  of  continu- 
ous flow  of  a  fluid,  as  distinguished  from  eddying  flow,  where  discontinuity 
takes  place. 

STREAMLINE-SHAPE — A  shape  intended  to  avoid  eddying  or  discon- 
tinuity and  to  preserve  streamline-flow,  thus  keeping  resistance  to  progress 
at  a  minimum. 

STRINGERS — A  term  applied  to  the  slender  wooden  members  running  lat- 
erally through  the  wing  ribs  for  the  purpose  of  stiffening  them. 
STRUT — A  compression  member  of  a  truss  frame,  for  instance,  the  vertical 
members  of  the  wing  truss  of  a  biplane. 

STRUT-INTERPLANE— A  strut  holding  apart  two  aerofoils. 
SUPPORTING  SURFACE— Any  surface  of  an  airplane  on  which   the  air 
produces  a  lift  reaction. 

SUSPENSION  BAND— The  band  around  a  balloon  to  which  are  attached 
the  basket  and  the  main  bridle  suspensions. 

SUSPENSION  BAR— The  bar  used  for  the  concentration  of  basket  suspen- 
sion ropes  in  captive  balloons. 

SWEEP-BACK — The   horizontal   angle   between    the    lateral    (athwartship) 
axis  of  an  airplane  and  the  entering  edge  of  the  main  planes. 
TACHOMETER — An  instrument  for  indicating  the  number  of  revolutions 
per  minute  of  the  engine  or  propeller. 

TAIL  CUPS — The  steadying  device  attached  at  the  rear  of  certain  types  of 
elongated  captive  balloons. 

TAIL-NEUTRAL — A  tail,  the  horizontal  stabilizer  of  which  is  so  set  that  it 
gives  neither  an  upward  lift  nor  a  downward  thrust  when  the  machine  is  in 
normal  flight. 

Positive — A  tail  in  which  the  horizontal  stabilizer  is  so  set  as  to  give  an 
upward  lift  and  thus  assist  in  carrying  the  weight  of  the  airplane  when 
it  is  in  normal  flight. 

Negative — One  in  which  the  horizontal  stabilizer  is  so  set  as  to  give  a 
downward  thrust  on  the  tail  when  the  machine  is  in  normal  flight. 


NOMENCLATURE  FOR  AERONAUTICS  119 

TAIL  POST— The  vertical  strut  at  the  rear  end  of  the  fuselage. 

TAIL  SKID — A  skid  su])|)()rtiiii;-  the  tail  of  a  fuselas^e  wliile  on  the  ground. 

TAIL  SLIDE — A  steep  descent,  tail  downward.     I'sually  caused  by  stalling 
on  an  attenij)t  to  climb  too  steeply. 

THIMBLE — An  elongated  metal  eye  s])lice(l  in  the  end  of  a  ro[)e  or  cable. 

TRACTOR— (See  AIRPLANE.) 

TRAILING  EDGE — The  rearmost  ])ortion  of  an  aerofoil. 

TRIPLANE — A  form  of  airplane  whose  main  supporting  surface  is  divided 

into  three  jjarts,  superimposed. 

TRUSS — The  framing  by  wiiicli  the  wing  loads  are  transmitted  to  the  body; 
comprises  struts,  stays  and  spars. 

UNDERCARRIAGE— (See  LANDING  GEAR.) 

VETTING — The  process  of  sighting  by  eye  along  edges  of  spars,  planes,  etc., 

to  ascertain  their  alignment.     An   experienced  man  can   detect  and  remedy 

many  faults  in  alignment  by  this  method. 

VOL-PIQUE'— (See  NOSE  DIVE.) 

VOLPLANE— To  glide. 

WARP — To  change  the  form  of  the  wing  by  twisting  it,  usually  by  changing 

the  inclination  of  the  rear  spar  relative  to  the  front  spar. 

WASHIN — A  progressive  increase  in  the  angle  of  incidence  from  the  fusel- 
age toward  the  wing  tip. 

WASHOUT — A   i^rogressive   decrease    in    the   angle   of   incidence    from    the 
fuselage  toward  the  wing  tip. 

WEIGHT-GROSS— (See  LOAD,  FULL.) 

WINGS — The  main  supporting  surfaces  of  an  airplane.    Also  called  Aerofoils. 
WING  FLAPS— (See  AILERON.) 
WING  LOADING— (See  LOADING.) 

WING  MAST — The  mast  structure  projecting  above  the  wing,  to  which  the 
toj:)  load  wires  are  attached. 

WING  RIB — A  fore-and-aft  member  of  the  wing  structure  used  to  support 
the  covering  and  to  give  the  wing  section  its  form.     (See  RIB.) 
WING  SPAR  OR  WING  BEAM— A  transverse  member  of  the  wing  struc- 
ture.    (See  SPARS-WING.) 

WIRES— 

Drift — Wires  that  take  the  drift  load  and  transfer  it  through  various 
members  to  the  body  of  the  airplane. 

Flying — The  wires  that  transfer  to  the  fuselage,  the  forces  due  to  the 
lift  on  the  wings  when  an  airplane  is  in  flight.  They  prevent  the  wings 
from  collapsing  upwards  during  flight. 

Landing — The  wires  that  transfer  to  the  fuselage,  the  forces  due  to  the 
weight  of  the  wings  when  an  airjilane  is  landing  or  resting  on  the  ground. 
Stagger — The  cross  brace  wires  between  the  interplane  struts  in  a  fore- 
and-aft  direction. 


120  APPLIED  AERONAUTICS 

YAW — To  yaw  is  to  swing  off  the  course  and  turn  about  the  vertical  axis 
owing  to  side  gusts  of  wind  or  lack  of  directional  stability. 

Angle   Of — The   temi)orary   angular   deviation   of   the   fore-and-aft   axis 

from  the  course. 

Physical  and  Mechanical  Terms 

ACCELERATION— The  rate  of  increase  of  velocity. 

CENTER  OF   GRAVITY— The  center  of  gravity  of  a  body  is  that   point 

about  which,  if  suspended,  all  the  parts  will  be  in  ecpiilibrium,  that  is,  there 

will  be  no  tendency  to  rotation. 

CENTRIFUGAL   FORCE— That   force   which   urges   a   body,   moving   in   a 

curved  path,  outward  from  the  center  of  rotation. 

COMPONENT — A  force  which  when  combined  with  one  or  more  like  forces 

produces  the  effect  of  a  single  force.     The  single  force  is  regarded  as  the 

RESULTANT  of  the  component  forces. 

DENSITY — Mass  per  unit  of  volume;  for  instance,  pounds  per  cubic  foot. 

EFFICIENCY-(Of  a  machine.) — The  ratio  of  output  to  input  of  power,  usu- 
ally expressed  as  percentage. 

ELASTIC  LIMIT — The  greatest  stress  per  unit  area  which  will  not  produce 

a  permanent  deformation  of  the  material  under  str'ess. 

ELONGATION — When   any   material   fails  by  tension   it   usually   stretches 

and  takes  a  permanent  set  before  it  breaks.     The   ratio   of  this  permanent 

elongation  to  the  original  length,  expressed  as  a  percentage,  is  a  measure  of 

the  elongation. 

ENERGY — The  capacity  of  a  body  for  doing  work.    Heat  is  a  form  of  energy. 

Any   chemical   reaction   that   generates   heat   or   electricity   liberates    energy. 

Bodies  may  possess  energy  by  virtue  of  having  work  done  upon  them. 

EQUILIBRIUM — When  two  or  more  forces  act  upon  a  body  in  such  a  way 

that  no- motion  results,  there  is  said  to  be  equilibrium. 

FACTOR  OF  SAFETY— The  ratio  of  the  load  required  to  cause  failure  in 

a  structural  member  to  the  usual  working  load  the  member  is  designed  to 

carry.    Thus  if  a  member  be  designed  to  carry  a  load  of  500  lbs.  and  it  would 

require  a  load  of  2000  lbs.  to  cause  failure,  the  factor  of  safety  would  be  four. 

FOOT-POUND — The  foot-pound  is  a  unit  of  work.  It  is  equal  to  a  force  of  one 

pound  acting  through  a  distance  of  one  foot.    This  is  a  foot-pound  of  energy. 

INERTIA — That  property  of  a  body  by  virtue  of  which  it  resists  au}^  attempt 

to  start  it  if  at  rest,  to  stop  it  if  in  motion,  or  in  any  way  to  change  either 

the  direction  or  velocity  of  motion,  is  called  Inertia. 

MASS— The  mass  of  a  body  is  a  measure  of  the  quantity  of  material  in  it. 

MOMENT — Moment  is  the   product  of  ^a  force  times  its  lever  arm.     It  is 

usually  expressed  in  Inch-Pounds. 

MOMENTUM — Momentum   is   the  product  of  .the   mass  and   velocity  of  a 

moving  body.     It  is  a  measure  of  the  quantity  of  motion. 

POWER — Power  is  the  time  rate  of  doing  work. 

Horsepower — The  horsepower  is  a  unit  of  work.  One  horsepower  rep- 
resents the  performance  of  work  at  the  rate  of  33,000  foot-pounds  per 
minute,  or  550  foot-pounds  per  second. 


NOMENCLATURE  FOR  AERONAUTICS  121 

RESULTANT  OF  A  FORCE— 'I'lie  resultant  of  two  or  more  forces  is  that 
single  force  which  will  ])r()(luce  the  same  effect  upon  a  body  as  is  produced 
hv  the  joint  action  (if  the  component  forces. 

STRESS — The  internal  condition  of  a  body  under  the  actiijn  of  opposing- 
forces.     The  unit  of  measure  is  usually  |)Ounds  per  square  inch. 

Compression — When  forces  are  a])i)lied  to  a  Ixxly  in  such  a  way  as  to 

tend  to  crush  it,  there  results  a  compressive  stress  in  the  body. 

Tension — When  forces  are  ap])lied  to  a  body  in  such  a  way  as  to  tend  to 

se])arate  or  j)ull  it  apart,  the  l)ody  is  said  to  be  in  tensi(jn  or  a  tensile 

stress  has  been  j^rodnced  within  it. 

Shear — W'hen  external  forces  are  a])i)lic(l  in   such  a  way  as  to  cause  a 

tendency  for  particles  of  a  body  to  sli])  or  slide  ])ast  each  other,  there 

results  a  shearing'  stress  in  the  l)ody. 
STRAIN — Strain   is  the  deformation   jiroduced   in   a  body  by   the  a])i)lication 
of  external  forces. 

TORQUE — When  forces  are  so  disposed  as  to  cause  (jr  tend  to  cause  rotation, 
there  is  produced  a  turning'  moment  which  is  also  called  torque.  It  is  usually 
measured  in  inch-pounds.  Thus  if  a  force  of  10  pounds  be  applied  tangen- 
tiall}'  to  the  rim  of  a  wheel  of  10-incli  radixis.  the  torcjue  or  turning  moment 
will  be  100  inch-pounds. 

ULTIMATE  STRENGTH— The  load  per  s(juare  inch  required  to  produce 
fracture. 

VELOCITY — In  uniform  motion,  the  distance  passed  over  in  a  unit  of  time, 
as  one  second.  This  may  also  be  obtained  by  di\-iding  the  length  of  an\'  por- 
tion of  the  path  by  the  time  taken  to  describe  that  portion,  no  matter  how 
small  or  great. 

In  N'ariable  motion,  where  velocity  varies  from  point  to  point,  its  \'alue 
at  any  point  is  expressed  as  the  quotient  of  an  infinitely  small  distance,  con- 
taining the  given  point  by  the  inhniteh-  small  portion  of  time  in  which  this 
distance  is  described. 

WORK  —The  product  of  a  force  by  the  distance  descrilK'd  in  the  direction 
of  the  torce  by  the  point  of  application.  If  the  force  moves  forward  it  is 
called  a  working  force,  and  is  said  to  do  the  work  expressed  by  this  product; 
if  backward,  it  is  called  a  resistance,  and  is  then  said  to  have  the  work  done 
U])on  it,  in  overcoming"  the  resistance  through  the  distance  nientioned  (it 
might  also  be  said  to  have  done  negative  work). 

In  a  uniform  translation,  the  working  forces  do  an  amount  of  work  which 
is  entirely  a])plie(l  to  overcoming  the  resistances. 


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